diff --git a/src/Numerics/LinearAlgebra/Complex/Solvers/BiCgStab.cs b/src/Numerics/LinearAlgebra/Complex/Solvers/BiCgStab.cs
index 0474e696..fb22c8c2 100644
--- a/src/Numerics/LinearAlgebra/Complex/Solvers/BiCgStab.cs
+++ b/src/Numerics/LinearAlgebra/Complex/Solvers/BiCgStab.cs
@@ -30,7 +30,6 @@
 
 using System;
 using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using MathNet.Numerics.Properties;
 
 namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers
@@ -73,12 +72,6 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers
     /// </remarks>
     public sealed class BiCgStab : IIterativeSolver<Complex>
     {
-        /// <summary>
-        /// The status used if there is no status, i.e. the solver hasn't run yet and there is no
-        /// iterator.
-        /// </summary>
-        static readonly ICalculationStatus DefaultStatus = new CalculationIndetermined();
-
         /// <summary>
         /// The preconditioner that will be used. Can be set to <see langword="null" />, in which case the default
         /// pre-conditioner will be used.
@@ -188,9 +181,9 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers
         /// <summary>
         /// Gets the status of the iteration once the calculation is finished.
         /// </summary>
-        public ICalculationStatus IterationResult
+        public IterationStatus IterationResult
         {
-            get { return (_iterator != null) ? _iterator.Status : DefaultStatus; }
+            get { return (_iterator != null) ? _iterator.Status : IterationStatus.Indetermined; }
         }
 
         /// <summary>
@@ -470,7 +463,8 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers
                 return true;
             }
 
-            return !_iterator.DetermineStatus(iterationNumber, result, source, residuals).TerminatesCalculation;
+            var status = _iterator.DetermineStatus(iterationNumber, result, source, residuals);
+            return status == IterationStatus.Running || status == IterationStatus.Indetermined;
         }
 
         /// <summary>
diff --git a/src/Numerics/LinearAlgebra/Complex/Solvers/CompositeSolver.cs b/src/Numerics/LinearAlgebra/Complex/Solvers/CompositeSolver.cs
index 798ee066..bc8eb73c 100644
--- a/src/Numerics/LinearAlgebra/Complex/Solvers/CompositeSolver.cs
+++ b/src/Numerics/LinearAlgebra/Complex/Solvers/CompositeSolver.cs
@@ -34,7 +34,6 @@ using System.IO;
 using System.Linq;
 using System.Reflection;
 using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using MathNet.Numerics.Properties;
 
 namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers
@@ -94,16 +93,6 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers
 
         #endregion
 
-        /// <summary>
-        /// The default status used if the solver is not running.
-        /// </summary>
-        static readonly ICalculationStatus NonRunningStatus = new CalculationIndetermined();
-
-        /// <summary>
-        /// The default status used if the solver is running.
-        /// </summary>
-        static readonly ICalculationStatus RunningStatus = new CalculationRunning();
-
 #if PORTABLE
         private static readonly Dictionary<double, List<IIterativeSolverSetup<Complex>>> SolverSetups = new Dictionary<double, List<IIterativeSolverSetup<Complex>>>();        
 #else
@@ -348,7 +337,7 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers
         /// <summary>
         /// The status of the calculation.
         /// </summary>
-        ICalculationStatus _status = NonRunningStatus;
+        IterationStatus _status = IterationStatus.Indetermined;
 
         /// <summary>
         /// The iterator that is used to control the iteration process.
@@ -394,7 +383,7 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers
         /// <summary>
         /// Gets the status of the iteration once the calculation is finished.
         /// </summary>
-        public ICalculationStatus IterationResult
+        public IterationStatus IterationResult
         {
             get
             {
@@ -517,7 +506,7 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers
                     // Switch to the next preconditioner. 
                     // Reset the solution vector to the previous solution
                     input.CopyTo(internalInput);
-                    _status = RunningStatus;
+                    _status = IterationStatus.Running;
                     continue;
                 }
 
diff --git a/src/Numerics/LinearAlgebra/Complex/Solvers/GpBiCg.cs b/src/Numerics/LinearAlgebra/Complex/Solvers/GpBiCg.cs
index fabf3990..5830d0aa 100644
--- a/src/Numerics/LinearAlgebra/Complex/Solvers/GpBiCg.cs
+++ b/src/Numerics/LinearAlgebra/Complex/Solvers/GpBiCg.cs
@@ -30,7 +30,6 @@
 
 using System;
 using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using MathNet.Numerics.Properties;
 
 namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers
@@ -71,12 +70,6 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers
     /// </remarks>
     public sealed class GpBiCg : IIterativeSolver<Complex>
     {
-        /// <summary>
-        /// The status used if there is no status, i.e. the solver hasn't run yet and there is no
-        /// iterator.
-        /// </summary>
-        static readonly ICalculationStatus DefaultStatus = new CalculationIndetermined();
-
         /// <summary>
         /// The preconditioner that will be used. Can be set to <c>null</c>, in which case the default
         /// pre-conditioner will be used.
@@ -236,9 +229,9 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers
         /// <summary>
         /// Gets the status of the iteration once the calculation is finished.
         /// </summary>
-        public ICalculationStatus IterationResult
+        public IterationStatus IterationResult
         {
-            get { return (_iterator != null) ? _iterator.Status : DefaultStatus; }
+            get { return (_iterator != null) ? _iterator.Status : IterationStatus.Indetermined; }
         }
 
         /// <summary>
@@ -553,7 +546,8 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers
                 return true;
             }
 
-            return !_iterator.DetermineStatus(iterationNumber, result, source, residuals).TerminatesCalculation;
+            var status = _iterator.DetermineStatus(iterationNumber, result, source, residuals);
+            return status == IterationStatus.Running || status == IterationStatus.Indetermined;
         }
 
         /// <summary>
diff --git a/src/Numerics/LinearAlgebra/Complex/Solvers/MlkBiCgStab.cs b/src/Numerics/LinearAlgebra/Complex/Solvers/MlkBiCgStab.cs
index cd8acfec..72715d7e 100644
--- a/src/Numerics/LinearAlgebra/Complex/Solvers/MlkBiCgStab.cs
+++ b/src/Numerics/LinearAlgebra/Complex/Solvers/MlkBiCgStab.cs
@@ -34,7 +34,6 @@ using System.Diagnostics;
 using System.Linq;
 using MathNet.Numerics.Distributions;
 using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using MathNet.Numerics.Properties;
 
 namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers
@@ -77,12 +76,6 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers
         /// </summary>
         const int DefaultNumberOfStartingVectors = 50;
 
-        /// <summary>
-        /// The status used if there is no status, i.e. the solver hasn't run yet and there is no
-        /// iterator.
-        /// </summary>
-        static readonly ICalculationStatus DefaultStatus = new CalculationIndetermined();
-
         /// <summary>
         /// The preconditioner that will be used. Can be set to <see langword="null" />, in which case the default
         /// pre-conditioner will be used.
@@ -257,10 +250,10 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers
         /// <summary>
         /// Gets the status of the iteration once the calculation is finished.
         /// </summary>
-        public ICalculationStatus IterationResult
+        public IterationStatus IterationResult
         {
             [DebuggerStepThrough]
-            get { return (_iterator != null) ? _iterator.Status : DefaultStatus; }
+            get { return (_iterator != null) ? _iterator.Status : IterationStatus.Indetermined; }
         }
 
         /// <summary>
@@ -736,7 +729,8 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers
                 return true;
             }
 
-            return !_iterator.DetermineStatus(iterationNumber, result, source, residuals).TerminatesCalculation;
+            var status = _iterator.DetermineStatus(iterationNumber, result, source, residuals);
+            return status == IterationStatus.Running || status == IterationStatus.Indetermined;
         }
 
         /// <summary>
diff --git a/src/Numerics/LinearAlgebra/Complex/Solvers/StopCriterium/DivergenceStopCriterium.cs b/src/Numerics/LinearAlgebra/Complex/Solvers/StopCriterium/DivergenceStopCriterium.cs
index 4f8a5626..6bbfaa9c 100644
--- a/src/Numerics/LinearAlgebra/Complex/Solvers/StopCriterium/DivergenceStopCriterium.cs
+++ b/src/Numerics/LinearAlgebra/Complex/Solvers/StopCriterium/DivergenceStopCriterium.cs
@@ -29,7 +29,6 @@
 // </copyright>
 
 using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using System;
 using System.Diagnostics;
 
@@ -52,7 +51,7 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers.StopCriterium
         /// residual may experience before a divergence warning is issued.
         /// </summary>
         public const double DefaultMaximumRelativeIncrease = 0.08;
-        
+
         /// <summary>
         /// Default value for the minimum number of iterations over which 
         /// the residual must grow before a divergence warning is issued.
@@ -63,37 +62,32 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers.StopCriterium
         /// Defines the default last iteration number. Set to -1 because iterations normally
         /// start at 0.
         /// </summary>
-        private const int DefaultLastIterationNumber = -1;
+        const int DefaultLastIterationNumber = -1;
 
-        /// <summary>
-        /// The default status.
-        /// </summary>
-        private static readonly ICalculationStatus DefaultStatus = new CalculationIndetermined();
-        
         /// <summary>
         /// The maximum relative increase the residual may experience without triggering a divergence warning.
         /// </summary>
-        private double _maximumRelativeIncrease;
+        double _maximumRelativeIncrease;
 
         /// <summary>
         /// The number of iterations over which a residual increase should be tracked before issuing a divergence warning.
         /// </summary>
-        private int _minimumNumberOfIterations;
+        int _minimumNumberOfIterations;
 
         /// <summary>
         /// The status of the calculation
         /// </summary>
-        private ICalculationStatus _status = DefaultStatus;
+        IterationStatus _status = IterationStatus.Indetermined;
 
         /// <summary>
         /// The array that holds the tracking information.
         /// </summary>
-        private double[] _residualHistory;
+        double[] _residualHistory;
 
         /// <summary>
         /// The iteration number of the last iteration.
         /// </summary>
-        private int _lastIteration = DefaultLastIterationNumber;
+        int _lastIteration = DefaultLastIterationNumber;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="DivergenceStopCriterium"/> class with the default maximum 
@@ -117,7 +111,7 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers.StopCriterium
         /// relative increase and the specified minimum number of tracking iterations.
         /// </summary>
         /// <param name="minimumIterations">The minimum number of iterations over which the residual must grow before a divergence warning is issued. </param>
-        public DivergenceStopCriterium(int minimumIterations) : this(DefaultMinimumNumberOfIterations,  minimumIterations)
+        public DivergenceStopCriterium(int minimumIterations) : this(DefaultMinimumNumberOfIterations, minimumIterations)
         {
         }
 
@@ -224,18 +218,13 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers.StopCriterium
         /// on the invocation of this method. Therefore this method should only be called if the 
         /// calculation has moved forwards at least one step.
         /// </remarks>
-        public ICalculationStatus DetermineStatus(int iterationNumber, Vector<Complex> solutionVector, Vector<Complex> sourceVector, Vector<Complex> residualVector)
+        public IterationStatus DetermineStatus(int iterationNumber, Vector<Complex> solutionVector, Vector<Complex> sourceVector, Vector<Complex> residualVector)
         {
             if (iterationNumber < 0)
             {
                 throw new ArgumentOutOfRangeException("iterationNumber");
             }
 
-            if (residualVector == null)
-            {
-                throw new ArgumentNullException("residualVector");
-            }
-
             if (_lastIteration >= iterationNumber)
             {
                 // We have already stored the actual last iteration number
@@ -263,19 +252,12 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers.StopCriterium
             // Stop the iteration.
             if (double.IsNaN(_residualHistory[_residualHistory.Length - 1]))
             {
-                SetStatusToDiverged();
+                _status = IterationStatus.Diverged;
                 return _status;
             }
 
             // Check if we are diverging and if so set the status
-            if (IsDiverging())
-            {
-                SetStatusToDiverged();
-            }
-            else
-            {
-                SetStatusToRunning();
-            }
+            _status = IsDiverging() ? IterationStatus.Diverged : IterationStatus.Running;
 
             _lastIteration = iterationNumber;
             return _status;
@@ -285,7 +267,7 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers.StopCriterium
         /// Detect if solution is diverging
         /// </summary>
         /// <returns><c>true</c> if diverging, otherwise <c>false</c></returns>
-        private bool IsDiverging()
+        bool IsDiverging()
         {
             // Run for each variable
             for (var i = 1; i < _residualHistory.Length; i++)
@@ -295,7 +277,7 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers.StopCriterium
                 // Divergence is occurring if:
                 // - the last residual is larger than the previous one
                 // - the relative increase of the residual is larger than the setting allows
-                if ((difference < 0) || (_residualHistory[i - 1] * (1 + _maximumRelativeIncrease) >= _residualHistory[i]))
+                if ((difference < 0) || (_residualHistory[i - 1]*(1 + _maximumRelativeIncrease) >= _residualHistory[i]))
                 {
                     // No divergence taking place within the required number of iterations
                     // So reset and stop the iteration. There is no way we can get to the
@@ -310,7 +292,7 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers.StopCriterium
         /// <summary>
         /// Gets required history Length
         /// </summary>
-        private int RequiredHistoryLength
+        int RequiredHistoryLength
         {
             [DebuggerStepThrough]
             get
@@ -319,32 +301,10 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers.StopCriterium
             }
         }
 
-        /// <summary>
-        /// Set status to <see cref="CalculationDiverged"/>
-        /// </summary>
-        private void SetStatusToDiverged()
-        {
-            if (!(_status is CalculationDiverged))
-            {
-                _status = new CalculationDiverged();
-            }
-        }
-
-        /// <summary>
-        /// Set status to <see cref="CalculationRunning"/>
-        /// </summary>
-        private void SetStatusToRunning()
-        {
-            if (!(_status is CalculationRunning))
-            {
-                _status = new CalculationRunning();
-            }
-        }
-
         /// <summary>
         /// Gets the current calculation status.
         /// </summary>
-        public ICalculationStatus Status
+        public IterationStatus Status
         {
             [DebuggerStepThrough]
             get
@@ -358,7 +318,7 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers.StopCriterium
         /// </summary>
         public void ResetToPrecalculationState()
         {
-            _status = DefaultStatus;
+            _status = IterationStatus.Indetermined;
             _lastIteration = DefaultLastIterationNumber;
             _residualHistory = null;
         }
diff --git a/src/Numerics/LinearAlgebra/Complex/Solvers/StopCriterium/FailureStopCriterium.cs b/src/Numerics/LinearAlgebra/Complex/Solvers/StopCriterium/FailureStopCriterium.cs
index 7351cfa8..fda82649 100644
--- a/src/Numerics/LinearAlgebra/Complex/Solvers/StopCriterium/FailureStopCriterium.cs
+++ b/src/Numerics/LinearAlgebra/Complex/Solvers/StopCriterium/FailureStopCriterium.cs
@@ -28,11 +28,10 @@
 // OTHER DEALINGS IN THE SOFTWARE.
 // </copyright>
 
-using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
-using MathNet.Numerics.Properties;
 using System;
 using System.Diagnostics;
+using MathNet.Numerics.LinearAlgebra.Solvers;
+using MathNet.Numerics.Properties;
 
 namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers.StopCriterium
 {
@@ -52,22 +51,17 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers.StopCriterium
         /// Defines the default last iteration number. Set to -1 because iterations normally
         /// start at 0.
         /// </summary>
-        private const int DefaultLastIterationNumber = -1;
-
-        /// <summary>
-        /// The default status.
-        /// </summary>
-        private static readonly ICalculationStatus DefaultStatus = new CalculationIndetermined();
+        const int DefaultLastIterationNumber = -1;
 
         /// <summary>
         /// The status of the calculation
         /// </summary>
-        private ICalculationStatus _status = DefaultStatus;
+        IterationStatus _status = IterationStatus.Indetermined;
 
         /// <summary>
         /// The iteration number of the last iteration.
         /// </summary>
-        private int _lastIteration = DefaultLastIterationNumber;
+        int _lastIteration = DefaultLastIterationNumber;
 
         /// <summary>
         /// Determines the status of the iterative calculation based on the stop criteria stored
@@ -82,23 +76,13 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers.StopCriterium
         /// on the invocation of this method. Therefore this method should only be called if the 
         /// calculation has moved forwards at least one step.
         /// </remarks>
-        public ICalculationStatus DetermineStatus(int iterationNumber, Vector<Complex> solutionVector, Vector<Complex> sourceVector, Vector<Complex> residualVector)
+        public IterationStatus DetermineStatus(int iterationNumber, Vector<Complex> solutionVector, Vector<Complex> sourceVector, Vector<Complex> residualVector)
         {
             if (iterationNumber < 0)
             {
                 throw new ArgumentOutOfRangeException("iterationNumber");
             }
 
-            if (solutionVector == null)
-            {
-                throw new ArgumentNullException("solutionVector");
-            }
-
-            if (residualVector == null)
-            {
-                throw new ArgumentNullException("residualVector");
-            }
-
             if (solutionVector.Count != residualVector.Count)
             {
                 throw new ArgumentException(Resources.ArgumentArraysSameLength);
@@ -115,45 +99,16 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers.StopCriterium
             var residualNorm = residualVector.InfinityNorm();
             var solutionNorm = solutionVector.InfinityNorm();
 
-            if (double.IsNaN(solutionNorm.Real) || double.IsNaN(residualNorm.Real))
-            {
-                SetStatusToFailed();
-            }
-            else
-            {
-                SetStatusToRunning();
-            }
+            _status = double.IsNaN(solutionNorm.Real) || double.IsNaN(residualNorm.Real) ? IterationStatus.Failure : IterationStatus.Running;
 
             _lastIteration = iterationNumber;
             return _status;
         }
 
-        /// <summary>
-        /// Set status to <see cref="CalculationFailure"/>
-        /// </summary>
-        private void SetStatusToFailed()
-        {
-            if (!(_status is CalculationFailure))
-            {
-                _status = new CalculationFailure();
-            }
-        }
-
-        /// <summary>
-        /// Set status to <see cref="CalculationRunning"/>
-        /// </summary>
-        private void SetStatusToRunning()
-        {
-            if (!(_status is CalculationRunning))
-            {
-                _status = new CalculationRunning();
-            }
-        }
-
         /// <summary>
         /// Gets the current calculation status.
         /// </summary>
-        public ICalculationStatus Status
+        public IterationStatus Status
         {
             [DebuggerStepThrough]
             get
@@ -167,7 +122,7 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers.StopCriterium
         /// </summary>
         public void ResetToPrecalculationState()
         {
-            _status = DefaultStatus;
+            _status = IterationStatus.Indetermined;
             _lastIteration = DefaultLastIterationNumber;
         }
 
diff --git a/src/Numerics/LinearAlgebra/Complex/Solvers/StopCriterium/ResidualStopCriterium.cs b/src/Numerics/LinearAlgebra/Complex/Solvers/StopCriterium/ResidualStopCriterium.cs
index 2a66ac40..42b867ab 100644
--- a/src/Numerics/LinearAlgebra/Complex/Solvers/StopCriterium/ResidualStopCriterium.cs
+++ b/src/Numerics/LinearAlgebra/Complex/Solvers/StopCriterium/ResidualStopCriterium.cs
@@ -28,11 +28,10 @@
 // OTHER DEALINGS IN THE SOFTWARE.
 // </copyright>
 
-using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
-using MathNet.Numerics.Properties;
 using System;
 using System.Diagnostics;
+using MathNet.Numerics.LinearAlgebra.Solvers;
+using MathNet.Numerics.Properties;
 
 namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers.StopCriterium
 {
@@ -61,38 +60,33 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers.StopCriterium
         /// <summary>
         /// Defines the default last iteration number. Set to -1 because iterations normally start at 0.
         /// </summary>
-        private const int DefaultLastIterationNumber = -1;
-
-        /// <summary>
-        /// The default status.
-        /// </summary>
-        private static readonly ICalculationStatus DefaultStatus = new CalculationIndetermined();
+        const int DefaultLastIterationNumber = -1;
 
         /// <summary>
         /// The maximum value for the residual below which the calculation is considered converged.
         /// </summary>
-        private double _maximum;
+        double _maximum;
 
         /// <summary>
         /// The minimum number of iterations for which the residual has to be below the maximum before
         /// the calculation is considered converged.
         /// </summary>
-        private int _minimumIterationsBelowMaximum;
+        int _minimumIterationsBelowMaximum;
 
         /// <summary>
         /// The status of the calculation
         /// </summary>
-        private ICalculationStatus _status = DefaultStatus;
+        IterationStatus _status = IterationStatus.Indetermined;
 
         /// <summary>
         /// The number of iterations since the residuals got below the maximum.
         /// </summary>
-        private int _iterationCount;
+        int _iterationCount;
 
         /// <summary>
         /// The iteration number of the last iteration.
         /// </summary>
-        private int _lastIteration = DefaultLastIterationNumber;
+        int _lastIteration = DefaultLastIterationNumber;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="ResidualStopCriterium"/> class with the default maximum 
@@ -229,28 +223,13 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers.StopCriterium
         /// on the invocation of this method. Therefore this method should only be called if the 
         /// calculation has moved forwards at least one step.
         /// </remarks>
-        public ICalculationStatus DetermineStatus(int iterationNumber, Vector<Complex> solutionVector, Vector<Complex> sourceVector, Vector<Complex> residualVector)
+        public IterationStatus DetermineStatus(int iterationNumber, Vector<Complex> solutionVector, Vector<Complex> sourceVector, Vector<Complex> residualVector)
         {
             if (iterationNumber < 0)
             {
                 throw new ArgumentOutOfRangeException("iterationNumber");
             }
 
-            if (solutionVector == null)
-            {
-                throw new ArgumentNullException("solutionVector");
-            }
-
-            if (sourceVector == null)
-            {
-                throw new ArgumentNullException("sourceVector");
-            }
-            
-            if (residualVector == null)
-            {
-                throw new ArgumentNullException("residualVector");
-            }
-
             if (solutionVector.Count != sourceVector.Count)
             {
                 throw new ArgumentException(Resources.ArgumentVectorsSameLength, "sourceVector");
@@ -265,7 +244,7 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers.StopCriterium
             // These values will be used to calculate the relative drop in residuals
             // later on.
             var residualNorm = residualVector.InfinityNorm();
-            
+
             // Check the residuals by calculating:
             // ||r_i|| <= stop_tol * ||b||
             var stopCriterium = ComputeStopCriterium(sourceVector.InfinityNorm().Real);
@@ -276,7 +255,7 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers.StopCriterium
             if (double.IsNaN(stopCriterium) || double.IsNaN(residualNorm.Real))
             {
                 _iterationCount = 0;
-                SetStatusToDiverged();
+                _status = IterationStatus.Diverged;
                 return _status;
             }
 
@@ -288,20 +267,13 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers.StopCriterium
                 if (_lastIteration <= iterationNumber)
                 {
                     _iterationCount = iterationNumber - _lastIteration;
-                    if (_iterationCount >= _minimumIterationsBelowMaximum)
-                    {
-                        SetStatusToConverged();
-                    }
-                    else
-                    {
-                        SetStatusToRunning();
-                    }
+                    _status = _iterationCount >= _minimumIterationsBelowMaximum ? IterationStatus.Converged : IterationStatus.Running;
                 }
             }
             else
             {
                 _iterationCount = 0;
-                SetStatusToRunning();
+                _status = IterationStatus.Running;
             }
 
             _lastIteration = iterationNumber;
@@ -313,7 +285,7 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers.StopCriterium
         /// </summary>
         /// <param name="solutionNorm">Solution vector norm</param>
         /// <returns>Criterium value</returns>
-        private double ComputeStopCriterium(double solutionNorm)
+        double ComputeStopCriterium(double solutionNorm)
         {
             // This is criterium 1 from Templates for the solution of linear systems.
             // The problem with this criterium is that it's not limiting enough. For now 
@@ -321,46 +293,13 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers.StopCriterium
             // return mMaximumResidual * (System.Math.Abs(mMatrixNorm) * System.Math.Abs(solutionNorm) + System.Math.Abs(mVectorNorm));
 
             // For now use criterium 2 from Templates for the solution of linear systems. See page 60.
-            return _maximum * Math.Abs(solutionNorm);
-        }
-
-        /// <summary>
-        /// Set status to <see cref="CalculationDiverged"/>
-        /// </summary>
-        private void SetStatusToDiverged()
-        {
-            if (!(_status is CalculationDiverged))
-            {
-                _status = new CalculationDiverged();
-            }
-        }
-
-        /// <summary>
-        /// Set status to <see cref="CalculationConverged"/>
-        /// </summary>
-        private void SetStatusToConverged()
-        {
-            if (!(_status is CalculationConverged))
-            {
-                _status = new CalculationConverged();
-            }
-        }
-
-        /// <summary>
-        /// Set status to <see cref="CalculationRunning"/>
-        /// </summary>
-        private void SetStatusToRunning()
-        {
-            if (!(_status is CalculationRunning))
-            {
-                _status = new CalculationRunning();
-            }
+            return _maximum*Math.Abs(solutionNorm);
         }
 
         /// <summary>
         /// Gets the current calculation status.
         /// </summary>
-        public ICalculationStatus Status
+        public IterationStatus Status
         {
             [DebuggerStepThrough]
             get
@@ -374,7 +313,7 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers.StopCriterium
         /// </summary>
         public void ResetToPrecalculationState()
         {
-            _status = DefaultStatus;
+            _status = IterationStatus.Indetermined;
             _iterationCount = 0;
             _lastIteration = DefaultLastIterationNumber;
         }
diff --git a/src/Numerics/LinearAlgebra/Complex/Solvers/TFQMR.cs b/src/Numerics/LinearAlgebra/Complex/Solvers/TFQMR.cs
index f5e467c1..9750802a 100644
--- a/src/Numerics/LinearAlgebra/Complex/Solvers/TFQMR.cs
+++ b/src/Numerics/LinearAlgebra/Complex/Solvers/TFQMR.cs
@@ -30,7 +30,6 @@
 
 using System;
 using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using MathNet.Numerics.Properties;
 
 namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers
@@ -62,12 +61,6 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers
     /// </remarks>
     public sealed class TFQMR : IIterativeSolver<Complex>
     {
-        /// <summary>
-        /// The status used if there is no status, i.e. the solver hasn't run yet and there is no
-        /// iterator.
-        /// </summary>
-        static readonly ICalculationStatus DefaultStatus = new CalculationIndetermined();
-
         /// <summary>
         /// The preconditioner that will be used. Can be set to <see langword="null" />, in which case the default
         /// pre-conditioner will be used.
@@ -177,9 +170,9 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers
         /// <summary>
         /// Gets the status of the iteration once the calculation is finished.
         /// </summary>
-        public ICalculationStatus IterationResult
+        public IterationStatus IterationResult
         {
-            get { return (_iterator != null) ? _iterator.Status : DefaultStatus; }
+            get { return (_iterator != null) ? _iterator.Status : IterationStatus.Indetermined; }
         }
 
         /// <summary>
@@ -460,7 +453,8 @@ namespace MathNet.Numerics.LinearAlgebra.Complex.Solvers
                 return true;
             }
 
-            return !_iterator.DetermineStatus(iterationNumber, result, source, residuals).TerminatesCalculation;
+            var status = _iterator.DetermineStatus(iterationNumber, result, source, residuals);
+            return status == IterationStatus.Running || status == IterationStatus.Indetermined;
         }
 
         /// <summary>
diff --git a/src/Numerics/LinearAlgebra/Complex32/Solvers/BiCgStab.cs b/src/Numerics/LinearAlgebra/Complex32/Solvers/BiCgStab.cs
index dcaff85d..44a9cc7f 100644
--- a/src/Numerics/LinearAlgebra/Complex32/Solvers/BiCgStab.cs
+++ b/src/Numerics/LinearAlgebra/Complex32/Solvers/BiCgStab.cs
@@ -30,7 +30,6 @@
 
 using System;
 using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using MathNet.Numerics.Properties;
 
 namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers
@@ -66,12 +65,6 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers
     /// </remarks>
     public sealed class BiCgStab : IIterativeSolver<Numerics.Complex32>
     {
-        /// <summary>
-        /// The status used if there is no status, i.e. the solver hasn't run yet and there is no
-        /// iterator.
-        /// </summary>
-        static readonly ICalculationStatus DefaultStatus = new CalculationIndetermined();
-
         /// <summary>
         /// The preconditioner that will be used. Can be set to <see langword="null" />, in which case the default
         /// pre-conditioner will be used.
@@ -181,9 +174,9 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers
         /// <summary>
         /// Gets the status of the iteration once the calculation is finished.
         /// </summary>
-        public ICalculationStatus IterationResult
+        public IterationStatus IterationResult
         {
-            get { return (_iterator != null) ? _iterator.Status : DefaultStatus; }
+            get { return (_iterator != null) ? _iterator.Status : IterationStatus.Indetermined; }
         }
 
         /// <summary>
@@ -463,7 +456,8 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers
                 return true;
             }
 
-            return !_iterator.DetermineStatus(iterationNumber, result, source, residuals).TerminatesCalculation;
+            var status = _iterator.DetermineStatus(iterationNumber, result, source, residuals);
+            return status == IterationStatus.Running || status == IterationStatus.Indetermined;
         }
 
         /// <summary>
diff --git a/src/Numerics/LinearAlgebra/Complex32/Solvers/CompositeSolver.cs b/src/Numerics/LinearAlgebra/Complex32/Solvers/CompositeSolver.cs
index 07145609..56a675ff 100644
--- a/src/Numerics/LinearAlgebra/Complex32/Solvers/CompositeSolver.cs
+++ b/src/Numerics/LinearAlgebra/Complex32/Solvers/CompositeSolver.cs
@@ -34,7 +34,6 @@ using System.IO;
 using System.Linq;
 using System.Reflection;
 using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using MathNet.Numerics.Properties;
 
 namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers
@@ -86,16 +85,6 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers
 
         #endregion
 
-        /// <summary>
-        /// The default status used if the solver is not running.
-        /// </summary>
-        static readonly ICalculationStatus NonRunningStatus = new CalculationIndetermined();
-
-        /// <summary>
-        /// The default status used if the solver is running.
-        /// </summary>
-        static readonly ICalculationStatus RunningStatus = new CalculationRunning();
-
 #if PORTABLE
         private static readonly Dictionary<double, List<IIterativeSolverSetup<Complex32>>> SolverSetups = new Dictionary<double, List<IIterativeSolverSetup<Complex32>>>();        
 #else
@@ -340,7 +329,7 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers
         /// <summary>
         /// The status of the calculation.
         /// </summary>
-        ICalculationStatus _status = NonRunningStatus;
+        IterationStatus _status = IterationStatus.Indetermined;
 
         /// <summary>
         /// The iterator that is used to control the iteration process.
@@ -386,7 +375,7 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers
         /// <summary>
         /// Gets the status of the iteration once the calculation is finished.
         /// </summary>
-        public ICalculationStatus IterationResult
+        public IterationStatus IterationResult
         {
             get
             {
@@ -509,7 +498,7 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers
                     // Switch to the next preconditioner. 
                     // Reset the solution vector to the previous solution
                     input.CopyTo(internalInput);
-                    _status = RunningStatus;
+                    _status = IterationStatus.Running;
                     continue;
                 }
 
diff --git a/src/Numerics/LinearAlgebra/Complex32/Solvers/GpBiCg.cs b/src/Numerics/LinearAlgebra/Complex32/Solvers/GpBiCg.cs
index fdbd57b7..eef09eb2 100644
--- a/src/Numerics/LinearAlgebra/Complex32/Solvers/GpBiCg.cs
+++ b/src/Numerics/LinearAlgebra/Complex32/Solvers/GpBiCg.cs
@@ -30,7 +30,6 @@
 
 using System;
 using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using MathNet.Numerics.Properties;
 
 namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers
@@ -64,12 +63,6 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers
     /// </remarks>
     public sealed class GpBiCg : IIterativeSolver<Numerics.Complex32>
     {
-        /// <summary>
-        /// The status used if there is no status, i.e. the solver hasn't run yet and there is no
-        /// iterator.
-        /// </summary>
-        static readonly ICalculationStatus DefaultStatus = new CalculationIndetermined();
-
         /// <summary>
         /// The preconditioner that will be used. Can be set to <c>null</c>, in which case the default
         /// pre-conditioner will be used.
@@ -229,9 +222,9 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers
         /// <summary>
         /// Gets the status of the iteration once the calculation is finished.
         /// </summary>
-        public ICalculationStatus IterationResult
+        public IterationStatus IterationResult
         {
-            get { return (_iterator != null) ? _iterator.Status : DefaultStatus; }
+            get { return (_iterator != null) ? _iterator.Status : IterationStatus.Indetermined; }
         }
 
         /// <summary>
@@ -551,7 +544,8 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers
                 return true;
             }
 
-            return !_iterator.DetermineStatus(iterationNumber, result, source, residuals).TerminatesCalculation;
+            var status = _iterator.DetermineStatus(iterationNumber, result, source, residuals);
+            return status == IterationStatus.Running || status == IterationStatus.Indetermined;
         }
 
         /// <summary>
diff --git a/src/Numerics/LinearAlgebra/Complex32/Solvers/MlkBiCgStab.cs b/src/Numerics/LinearAlgebra/Complex32/Solvers/MlkBiCgStab.cs
index 9c5b4c3c..18c0ef03 100644
--- a/src/Numerics/LinearAlgebra/Complex32/Solvers/MlkBiCgStab.cs
+++ b/src/Numerics/LinearAlgebra/Complex32/Solvers/MlkBiCgStab.cs
@@ -34,7 +34,6 @@ using System.Diagnostics;
 using System.Linq;
 using MathNet.Numerics.Distributions;
 using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using MathNet.Numerics.Properties;
 
 namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers
@@ -69,12 +68,6 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers
         /// </summary>
         const int DefaultNumberOfStartingVectors = 50;
 
-        /// <summary>
-        /// The status used if there is no status, i.e. the solver hasn't run yet and there is no
-        /// iterator.
-        /// </summary>
-        static readonly ICalculationStatus DefaultStatus = new CalculationIndetermined();
-
         /// <summary>
         /// The preconditioner that will be used. Can be set to <see langword="null" />, in which case the default
         /// pre-conditioner will be used.
@@ -249,10 +242,10 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers
         /// <summary>
         /// Gets the status of the iteration once the calculation is finished.
         /// </summary>
-        public ICalculationStatus IterationResult
+        public IterationStatus IterationResult
         {
             [DebuggerStepThrough]
-            get { return (_iterator != null) ? _iterator.Status : DefaultStatus; }
+            get { return (_iterator != null) ? _iterator.Status : IterationStatus.Indetermined; }
         }
 
         /// <summary>
@@ -733,7 +726,8 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers
                 return true;
             }
 
-            return !_iterator.DetermineStatus(iterationNumber, result, source, residuals).TerminatesCalculation;
+            var status = _iterator.DetermineStatus(iterationNumber, result, source, residuals);
+            return status == IterationStatus.Running || status == IterationStatus.Indetermined;
         }
 
         /// <summary>
diff --git a/src/Numerics/LinearAlgebra/Complex32/Solvers/StopCriterium/DivergenceStopCriterium.cs b/src/Numerics/LinearAlgebra/Complex32/Solvers/StopCriterium/DivergenceStopCriterium.cs
index 97fbac8c..4b548bdd 100644
--- a/src/Numerics/LinearAlgebra/Complex32/Solvers/StopCriterium/DivergenceStopCriterium.cs
+++ b/src/Numerics/LinearAlgebra/Complex32/Solvers/StopCriterium/DivergenceStopCriterium.cs
@@ -29,7 +29,6 @@
 // </copyright>
 
 using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using System;
 using System.Diagnostics;
 
@@ -47,7 +46,7 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers.StopCriterium
         /// residual may experience before a divergence warning is issued.
         /// </summary>
         public const double DefaultMaximumRelativeIncrease = 0.08;
-        
+
         /// <summary>
         /// Default value for the minimum number of iterations over which 
         /// the residual must grow before a divergence warning is issued.
@@ -58,37 +57,32 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers.StopCriterium
         /// Defines the default last iteration number. Set to -1 because iterations normally
         /// start at 0.
         /// </summary>
-        private const int DefaultLastIterationNumber = -1;
+        const int DefaultLastIterationNumber = -1;
 
-        /// <summary>
-        /// The default status.
-        /// </summary>
-        private static readonly ICalculationStatus DefaultStatus = new CalculationIndetermined();
-        
         /// <summary>
         /// The maximum relative increase the residual may experience without triggering a divergence warning.
         /// </summary>
-        private double _maximumRelativeIncrease;
+        double _maximumRelativeIncrease;
 
         /// <summary>
         /// The number of iterations over which a residual increase should be tracked before issuing a divergence warning.
         /// </summary>
-        private int _minimumNumberOfIterations;
+        int _minimumNumberOfIterations;
 
         /// <summary>
         /// The status of the calculation
         /// </summary>
-        private ICalculationStatus _status = DefaultStatus;
+        IterationStatus _status = IterationStatus.Indetermined;
 
         /// <summary>
         /// The array that holds the tracking information.
         /// </summary>
-        private double[] _residualHistory;
+        double[] _residualHistory;
 
         /// <summary>
         /// The iteration number of the last iteration.
         /// </summary>
-        private int _lastIteration = DefaultLastIterationNumber;
+        int _lastIteration = DefaultLastIterationNumber;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="DivergenceStopCriterium"/> class with the default maximum 
@@ -112,7 +106,7 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers.StopCriterium
         /// relative increase and the specified minimum number of tracking iterations.
         /// </summary>
         /// <param name="minimumIterations">The minimum number of iterations over which the residual must grow before a divergence warning is issued. </param>
-        public DivergenceStopCriterium(int minimumIterations) : this(DefaultMinimumNumberOfIterations,  minimumIterations)
+        public DivergenceStopCriterium(int minimumIterations) : this(DefaultMinimumNumberOfIterations, minimumIterations)
         {
         }
 
@@ -219,18 +213,13 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers.StopCriterium
         /// on the invocation of this method. Therefore this method should only be called if the 
         /// calculation has moved forwards at least one step.
         /// </remarks>
-        public ICalculationStatus DetermineStatus(int iterationNumber, Vector<Complex32> solutionVector, Vector<Complex32> sourceVector, Vector<Complex32> residualVector)
+        public IterationStatus DetermineStatus(int iterationNumber, Vector<Complex32> solutionVector, Vector<Complex32> sourceVector, Vector<Complex32> residualVector)
         {
             if (iterationNumber < 0)
             {
                 throw new ArgumentOutOfRangeException("iterationNumber");
             }
 
-            if (residualVector == null)
-            {
-                throw new ArgumentNullException("residualVector");
-            }
-
             if (_lastIteration >= iterationNumber)
             {
                 // We have already stored the actual last iteration number
@@ -258,19 +247,12 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers.StopCriterium
             // Stop the iteration.
             if (double.IsNaN(_residualHistory[_residualHistory.Length - 1]))
             {
-                SetStatusToDiverged();
+                _status = IterationStatus.Diverged;
                 return _status;
             }
 
             // Check if we are diverging and if so set the status
-            if (IsDiverging())
-            {
-                SetStatusToDiverged();
-            }
-            else
-            {
-                SetStatusToRunning();
-            }
+            _status = IsDiverging() ? IterationStatus.Diverged : IterationStatus.Running;
 
             _lastIteration = iterationNumber;
             return _status;
@@ -280,7 +262,7 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers.StopCriterium
         /// Detect if solution is diverging
         /// </summary>
         /// <returns><c>true</c> if diverging, otherwise <c>false</c></returns>
-        private bool IsDiverging()
+        bool IsDiverging()
         {
             // Run for each variable
             for (var i = 1; i < _residualHistory.Length; i++)
@@ -290,7 +272,7 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers.StopCriterium
                 // Divergence is occurring if:
                 // - the last residual is larger than the previous one
                 // - the relative increase of the residual is larger than the setting allows
-                if ((difference < 0) || (_residualHistory[i - 1] * (1 + _maximumRelativeIncrease) >= _residualHistory[i]))
+                if ((difference < 0) || (_residualHistory[i - 1]*(1 + _maximumRelativeIncrease) >= _residualHistory[i]))
                 {
                     // No divergence taking place within the required number of iterations
                     // So reset and stop the iteration. There is no way we can get to the
@@ -305,7 +287,7 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers.StopCriterium
         /// <summary>
         /// Gets required history Length
         /// </summary>
-        private int RequiredHistoryLength
+        int RequiredHistoryLength
         {
             [DebuggerStepThrough]
             get
@@ -314,32 +296,10 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers.StopCriterium
             }
         }
 
-        /// <summary>
-        /// Set status to <see cref="CalculationDiverged"/>
-        /// </summary>
-        private void SetStatusToDiverged()
-        {
-            if (!(_status is CalculationDiverged))
-            {
-                _status = new CalculationDiverged();
-            }
-        }
-
-        /// <summary>
-        /// Set status to <see cref="CalculationRunning"/>
-        /// </summary>
-        private void SetStatusToRunning()
-        {
-            if (!(_status is CalculationRunning))
-            {
-                _status = new CalculationRunning();
-            }
-        }
-
         /// <summary>
         /// Gets the current calculation status.
         /// </summary>
-        public ICalculationStatus Status
+        public IterationStatus Status
         {
             [DebuggerStepThrough]
             get
@@ -353,7 +313,7 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers.StopCriterium
         /// </summary>
         public void ResetToPrecalculationState()
         {
-            _status = DefaultStatus;
+            _status = IterationStatus.Indetermined;
             _lastIteration = DefaultLastIterationNumber;
             _residualHistory = null;
         }
diff --git a/src/Numerics/LinearAlgebra/Complex32/Solvers/StopCriterium/FailureStopCriterium.cs b/src/Numerics/LinearAlgebra/Complex32/Solvers/StopCriterium/FailureStopCriterium.cs
index a881e558..67e57ef6 100644
--- a/src/Numerics/LinearAlgebra/Complex32/Solvers/StopCriterium/FailureStopCriterium.cs
+++ b/src/Numerics/LinearAlgebra/Complex32/Solvers/StopCriterium/FailureStopCriterium.cs
@@ -28,11 +28,10 @@
 // OTHER DEALINGS IN THE SOFTWARE.
 // </copyright>
 
-using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
-using MathNet.Numerics.Properties;
 using System;
 using System.Diagnostics;
+using MathNet.Numerics.LinearAlgebra.Solvers;
+using MathNet.Numerics.Properties;
 
 namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers.StopCriterium
 {
@@ -47,22 +46,17 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers.StopCriterium
         /// Defines the default last iteration number. Set to -1 because iterations normally
         /// start at 0.
         /// </summary>
-        private const int DefaultLastIterationNumber = -1;
-
-        /// <summary>
-        /// The default status.
-        /// </summary>
-        private static readonly ICalculationStatus DefaultStatus = new CalculationIndetermined();
+        const int DefaultLastIterationNumber = -1;
 
         /// <summary>
         /// The status of the calculation
         /// </summary>
-        private ICalculationStatus _status = DefaultStatus;
+        IterationStatus _status = IterationStatus.Indetermined;
 
         /// <summary>
         /// The iteration number of the last iteration.
         /// </summary>
-        private int _lastIteration = DefaultLastIterationNumber;
+        int _lastIteration = DefaultLastIterationNumber;
 
         /// <summary>
         /// Determines the status of the iterative calculation based on the stop criteria stored
@@ -77,23 +71,13 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers.StopCriterium
         /// on the invocation of this method. Therefore this method should only be called if the 
         /// calculation has moved forwards at least one step.
         /// </remarks>
-        public ICalculationStatus DetermineStatus(int iterationNumber, Vector<Complex32> solutionVector, Vector<Complex32> sourceVector, Vector<Complex32> residualVector)
+        public IterationStatus DetermineStatus(int iterationNumber, Vector<Complex32> solutionVector, Vector<Complex32> sourceVector, Vector<Complex32> residualVector)
         {
             if (iterationNumber < 0)
             {
                 throw new ArgumentOutOfRangeException("iterationNumber");
             }
 
-            if (solutionVector == null)
-            {
-                throw new ArgumentNullException("solutionVector");
-            }
-
-            if (residualVector == null)
-            {
-                throw new ArgumentNullException("residualVector");
-            }
-
             if (solutionVector.Count != residualVector.Count)
             {
                 throw new ArgumentException(Resources.ArgumentArraysSameLength);
@@ -110,45 +94,16 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers.StopCriterium
             var residualNorm = residualVector.InfinityNorm();
             var solutionNorm = solutionVector.InfinityNorm();
 
-            if (float.IsNaN(solutionNorm.Real) || float.IsNaN(residualNorm.Real))
-            {
-                SetStatusToFailed();
-            }
-            else
-            {
-                SetStatusToRunning();
-            }
+            _status = float.IsNaN(solutionNorm.Real) || float.IsNaN(residualNorm.Real) ? IterationStatus.Failure : IterationStatus.Running;
 
             _lastIteration = iterationNumber;
             return _status;
         }
 
-        /// <summary>
-        /// Set status to <see cref="CalculationFailure"/>
-        /// </summary>
-        private void SetStatusToFailed()
-        {
-            if (!(_status is CalculationFailure))
-            {
-                _status = new CalculationFailure();
-            }
-        }
-
-        /// <summary>
-        /// Set status to <see cref="CalculationRunning"/>
-        /// </summary>
-        private void SetStatusToRunning()
-        {
-            if (!(_status is CalculationRunning))
-            {
-                _status = new CalculationRunning();
-            }
-        }
-
         /// <summary>
         /// Gets the current calculation status.
         /// </summary>
-        public ICalculationStatus Status
+        public IterationStatus Status
         {
             [DebuggerStepThrough]
             get
@@ -162,7 +117,7 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers.StopCriterium
         /// </summary>
         public void ResetToPrecalculationState()
         {
-            _status = DefaultStatus;
+            _status = IterationStatus.Indetermined;
             _lastIteration = DefaultLastIterationNumber;
         }
 
diff --git a/src/Numerics/LinearAlgebra/Complex32/Solvers/StopCriterium/ResidualStopCriterium.cs b/src/Numerics/LinearAlgebra/Complex32/Solvers/StopCriterium/ResidualStopCriterium.cs
index 8234ce0a..6e728da3 100644
--- a/src/Numerics/LinearAlgebra/Complex32/Solvers/StopCriterium/ResidualStopCriterium.cs
+++ b/src/Numerics/LinearAlgebra/Complex32/Solvers/StopCriterium/ResidualStopCriterium.cs
@@ -31,7 +31,6 @@
 using System;
 using System.Diagnostics;
 using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using MathNet.Numerics.Properties;
 
 namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers.StopCriterium
@@ -56,38 +55,33 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers.StopCriterium
         /// <summary>
         /// Defines the default last iteration number. Set to -1 because iterations normally start at 0.
         /// </summary>
-        private const int DefaultLastIterationNumber = -1;
-
-        /// <summary>
-        /// The default status.
-        /// </summary>
-        private static readonly ICalculationStatus DefaultStatus = new CalculationIndetermined();
+        const int DefaultLastIterationNumber = -1;
 
         /// <summary>
         /// The maximum value for the residual below which the calculation is considered converged.
         /// </summary>
-        private float _maximum;
+        float _maximum;
 
         /// <summary>
         /// The minimum number of iterations for which the residual has to be below the maximum before
         /// the calculation is considered converged.
         /// </summary>
-        private int _minimumIterationsBelowMaximum;
+        int _minimumIterationsBelowMaximum;
 
         /// <summary>
         /// The status of the calculation
         /// </summary>
-        private ICalculationStatus _status = DefaultStatus;
+        IterationStatus _status = IterationStatus.Indetermined;
 
         /// <summary>
         /// The number of iterations since the residuals got below the maximum.
         /// </summary>
-        private int _iterationCount;
+        int _iterationCount;
 
         /// <summary>
         /// The iteration number of the last iteration.
         /// </summary>
-        private int _lastIteration = DefaultLastIterationNumber;
+        int _lastIteration = DefaultLastIterationNumber;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="ResidualStopCriterium"/> class with the default maximum 
@@ -224,28 +218,13 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers.StopCriterium
         /// on the invocation of this method. Therefore this method should only be called if the 
         /// calculation has moved forwards at least one step.
         /// </remarks>
-        public ICalculationStatus DetermineStatus(int iterationNumber, Vector<Complex32> solutionVector, Vector<Complex32> sourceVector, Vector<Complex32> residualVector)
+        public IterationStatus DetermineStatus(int iterationNumber, Vector<Complex32> solutionVector, Vector<Complex32> sourceVector, Vector<Complex32> residualVector)
         {
             if (iterationNumber < 0)
             {
                 throw new ArgumentOutOfRangeException("iterationNumber");
             }
 
-            if (solutionVector == null)
-            {
-                throw new ArgumentNullException("solutionVector");
-            }
-
-            if (sourceVector == null)
-            {
-                throw new ArgumentNullException("sourceVector");
-            }
-            
-            if (residualVector == null)
-            {
-                throw new ArgumentNullException("residualVector");
-            }
-
             if (solutionVector.Count != sourceVector.Count)
             {
                 throw new ArgumentException(Resources.ArgumentVectorsSameLength, "sourceVector");
@@ -260,7 +239,7 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers.StopCriterium
             // These values will be used to calculate the relative drop in residuals
             // later on.
             var residualNorm = residualVector.InfinityNorm();
-            
+
             // Check the residuals by calculating:
             // ||r_i|| <= stop_tol * ||b||
             var stopCriterium = ComputeStopCriterium(sourceVector.InfinityNorm().Real);
@@ -271,7 +250,7 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers.StopCriterium
             if (float.IsNaN(stopCriterium) || float.IsNaN(residualNorm.Real))
             {
                 _iterationCount = 0;
-                SetStatusToDiverged();
+                _status = IterationStatus.Diverged;
                 return _status;
             }
 
@@ -283,20 +262,13 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers.StopCriterium
                 if (_lastIteration <= iterationNumber)
                 {
                     _iterationCount = iterationNumber - _lastIteration;
-                    if (_iterationCount >= _minimumIterationsBelowMaximum)
-                    {
-                        SetStatusToConverged();
-                    }
-                    else
-                    {
-                        SetStatusToRunning();
-                    }
+                    _status = _iterationCount >= _minimumIterationsBelowMaximum ? IterationStatus.Converged : IterationStatus.Running;
                 }
             }
             else
             {
                 _iterationCount = 0;
-                SetStatusToRunning();
+                _status = IterationStatus.Running;
             }
 
             _lastIteration = iterationNumber;
@@ -308,7 +280,7 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers.StopCriterium
         /// </summary>
         /// <param name="solutionNorm">Solution vector norm</param>
         /// <returns>Criterium value</returns>
-        private float ComputeStopCriterium(float solutionNorm)
+        float ComputeStopCriterium(float solutionNorm)
         {
             // This is criterium 1 from Templates for the solution of linear systems.
             // The problem with this criterium is that it's not limiting enough. For now 
@@ -316,46 +288,13 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers.StopCriterium
             // return mMaximumResidual * (System.Math.Abs(mMatrixNorm) * System.Math.Abs(solutionNorm) + System.Math.Abs(mVectorNorm));
 
             // For now use criterium 2 from Templates for the solution of linear systems. See page 60.
-            return _maximum * Math.Abs(solutionNorm);
-        }
-
-        /// <summary>
-        /// Set status to <see cref="CalculationDiverged"/>
-        /// </summary>
-        private void SetStatusToDiverged()
-        {
-            if (!(_status is CalculationDiverged))
-            {
-                _status = new CalculationDiverged();
-            }
-        }
-
-        /// <summary>
-        /// Set status to <see cref="CalculationConverged"/>
-        /// </summary>
-        private void SetStatusToConverged()
-        {
-            if (!(_status is CalculationConverged))
-            {
-                _status = new CalculationConverged();
-            }
-        }
-
-        /// <summary>
-        /// Set status to <see cref="CalculationRunning"/>
-        /// </summary>
-        private void SetStatusToRunning()
-        {
-            if (!(_status is CalculationRunning))
-            {
-                _status = new CalculationRunning();
-            }
+            return _maximum*Math.Abs(solutionNorm);
         }
 
         /// <summary>
         /// Gets the current calculation status.
         /// </summary>
-        public ICalculationStatus Status
+        public IterationStatus Status
         {
             [DebuggerStepThrough]
             get
@@ -369,7 +308,7 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers.StopCriterium
         /// </summary>
         public void ResetToPrecalculationState()
         {
-            _status = DefaultStatus;
+            _status = IterationStatus.Indetermined;
             _iterationCount = 0;
             _lastIteration = DefaultLastIterationNumber;
         }
diff --git a/src/Numerics/LinearAlgebra/Complex32/Solvers/TFQMR.cs b/src/Numerics/LinearAlgebra/Complex32/Solvers/TFQMR.cs
index 2f206bd0..b4cd55a0 100644
--- a/src/Numerics/LinearAlgebra/Complex32/Solvers/TFQMR.cs
+++ b/src/Numerics/LinearAlgebra/Complex32/Solvers/TFQMR.cs
@@ -30,7 +30,6 @@
 
 using System;
 using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using MathNet.Numerics.Properties;
 
 namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers
@@ -54,12 +53,6 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers
     /// </remarks>
     public sealed class TFQMR : IIterativeSolver<Numerics.Complex32>
     {
-        /// <summary>
-        /// The status used if there is no status, i.e. the solver hasn't run yet and there is no
-        /// iterator.
-        /// </summary>
-        static readonly ICalculationStatus DefaultStatus = new CalculationIndetermined();
-
         /// <summary>
         /// The preconditioner that will be used. Can be set to <see langword="null" />, in which case the default
         /// pre-conditioner will be used.
@@ -169,9 +162,9 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers
         /// <summary>
         /// Gets the status of the iteration once the calculation is finished.
         /// </summary>
-        public ICalculationStatus IterationResult
+        public IterationStatus IterationResult
         {
-            get { return (_iterator != null) ? _iterator.Status : DefaultStatus; }
+            get { return (_iterator != null) ? _iterator.Status : IterationStatus.Indetermined; }
         }
 
         /// <summary>
@@ -457,7 +450,8 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32.Solvers
                 return true;
             }
 
-            return !_iterator.DetermineStatus(iterationNumber, result, source, residuals).TerminatesCalculation;
+            var status = _iterator.DetermineStatus(iterationNumber, result, source, residuals);
+            return status == IterationStatus.Running || status == IterationStatus.Indetermined;
         }
 
         /// <summary>
diff --git a/src/Numerics/LinearAlgebra/Double/Solvers/BiCgStab.cs b/src/Numerics/LinearAlgebra/Double/Solvers/BiCgStab.cs
index 9f0b1c5b..bade9a6b 100644
--- a/src/Numerics/LinearAlgebra/Double/Solvers/BiCgStab.cs
+++ b/src/Numerics/LinearAlgebra/Double/Solvers/BiCgStab.cs
@@ -30,7 +30,6 @@
 
 using System;
 using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using MathNet.Numerics.Properties;
 
 namespace MathNet.Numerics.LinearAlgebra.Double.Solvers
@@ -66,12 +65,6 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers
     /// </remarks>
     public sealed class BiCgStab : IIterativeSolver<double>
     {
-        /// <summary>
-        /// The status used if there is no status, i.e. the solver hasn't run yet and there is no
-        /// iterator.
-        /// </summary>
-        static readonly ICalculationStatus DefaultStatus = new CalculationIndetermined();
-
         /// <summary>
         /// The preconditioner that will be used. Can be set to <see langword="null" />, in which case the default
         /// pre-conditioner will be used.
@@ -180,11 +173,11 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers
         /// <summary>
         /// Gets the status of the iteration once the calculation is finished.
         /// </summary>
-        public ICalculationStatus IterationResult
+        public IterationStatus IterationResult
         {
             get
             {
-                return (_iterator != null) ? _iterator.Status : DefaultStatus;
+                return (_iterator != null) ? _iterator.Status : IterationStatus.Indetermined;
             }
         }
 
@@ -465,7 +458,8 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers
                 return true;
             }
 
-            return !_iterator.DetermineStatus(iterationNumber, result, source, residuals).TerminatesCalculation;
+            var status = _iterator.DetermineStatus(iterationNumber, result, source, residuals);
+            return status == IterationStatus.Running || status == IterationStatus.Indetermined;
         }
 
         /// <summary>
diff --git a/src/Numerics/LinearAlgebra/Double/Solvers/CompositeSolver.cs b/src/Numerics/LinearAlgebra/Double/Solvers/CompositeSolver.cs
index 525e476a..3f0b4ce3 100644
--- a/src/Numerics/LinearAlgebra/Double/Solvers/CompositeSolver.cs
+++ b/src/Numerics/LinearAlgebra/Double/Solvers/CompositeSolver.cs
@@ -34,7 +34,6 @@ using System.IO;
 using System.Linq;
 using System.Reflection;
 using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using MathNet.Numerics.Properties;
 
 namespace MathNet.Numerics.LinearAlgebra.Double.Solvers
@@ -83,16 +82,6 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers
 
         #endregion
 
-        /// <summary>
-        /// The default status used if the solver is not running.
-        /// </summary>
-        static readonly ICalculationStatus NonRunningStatus = new CalculationIndetermined();
-
-        /// <summary>
-        /// The default status used if the solver is running.
-        /// </summary>
-        static readonly ICalculationStatus RunningStatus = new CalculationRunning();
-
 #if PORTABLE
         private static readonly Dictionary<double, List<IIterativeSolverSetup<double>>> SolverSetups = new Dictionary<double, List<IIterativeSolverSetup<double>>>();        
 #else
@@ -337,7 +326,7 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers
         /// <summary>
         /// The status of the calculation.
         /// </summary>
-        ICalculationStatus _status = NonRunningStatus;
+        IterationStatus _status = IterationStatus.Indetermined;
 
         /// <summary>
         /// The iterator that is used to control the iteration process.
@@ -383,7 +372,7 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers
         /// <summary>
         /// Gets the status of the iteration once the calculation is finished.
         /// </summary>
-        public ICalculationStatus IterationResult
+        public IterationStatus IterationResult
         {
             get
             {
@@ -506,7 +495,7 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers
                     // Switch to the next preconditioner. 
                     // Reset the solution vector to the previous solution
                     input.CopyTo(internalInput);
-                    _status = RunningStatus;
+                    _status = IterationStatus.Running;
                     continue;
                 }
 
diff --git a/src/Numerics/LinearAlgebra/Double/Solvers/GpBiCg.cs b/src/Numerics/LinearAlgebra/Double/Solvers/GpBiCg.cs
index 9409d225..b4a830cf 100644
--- a/src/Numerics/LinearAlgebra/Double/Solvers/GpBiCg.cs
+++ b/src/Numerics/LinearAlgebra/Double/Solvers/GpBiCg.cs
@@ -30,7 +30,6 @@
 
 using System;
 using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using MathNet.Numerics.Properties;
 
 namespace MathNet.Numerics.LinearAlgebra.Double.Solvers
@@ -64,12 +63,6 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers
     /// </remarks>
     public sealed class GpBiCg : IIterativeSolver<double>
     {
-        /// <summary>
-        /// The status used if there is no status, i.e. the solver hasn't run yet and there is no
-        /// iterator.
-        /// </summary>
-        static readonly ICalculationStatus DefaultStatus = new CalculationIndetermined();
-
         /// <summary>
         /// The preconditioner that will be used. Can be set to <c>null</c>, in which case the default
         /// pre-conditioner will be used.
@@ -234,11 +227,11 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers
         /// <summary>
         /// Gets the status of the iteration once the calculation is finished.
         /// </summary>
-        public ICalculationStatus IterationResult
+        public IterationStatus IterationResult
         {
             get
             {
-                return (_iterator != null) ? _iterator.Status : DefaultStatus;
+                return (_iterator != null) ? _iterator.Status : IterationStatus.Indetermined;
             }
         }
 
@@ -559,7 +552,8 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers
                 return true;
             }
 
-            return !_iterator.DetermineStatus(iterationNumber, result, source, residuals).TerminatesCalculation;
+            var status = _iterator.DetermineStatus(iterationNumber, result, source, residuals);
+            return status == IterationStatus.Running || status == IterationStatus.Indetermined;
         }
 
         /// <summary>
diff --git a/src/Numerics/LinearAlgebra/Double/Solvers/MlkBiCgStab.cs b/src/Numerics/LinearAlgebra/Double/Solvers/MlkBiCgStab.cs
index c703af30..9161e7e8 100644
--- a/src/Numerics/LinearAlgebra/Double/Solvers/MlkBiCgStab.cs
+++ b/src/Numerics/LinearAlgebra/Double/Solvers/MlkBiCgStab.cs
@@ -34,7 +34,6 @@ using System.Diagnostics;
 using System.Linq;
 using MathNet.Numerics.Distributions;
 using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using MathNet.Numerics.Properties;
 
 namespace MathNet.Numerics.LinearAlgebra.Double.Solvers
@@ -69,12 +68,6 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers
         /// </summary>
         const int DefaultNumberOfStartingVectors = 50;
 
-        /// <summary>
-        /// The status used if there is no status, i.e. the solver hasn't run yet and there is no
-        /// iterator.
-        /// </summary>
-        static readonly ICalculationStatus DefaultStatus = new CalculationIndetermined();
-
         /// <summary>
         /// The preconditioner that will be used. Can be set to <see langword="null" />, in which case the default
         /// pre-conditioner will be used.
@@ -254,12 +247,12 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers
         /// <summary>
         /// Gets the status of the iteration once the calculation is finished.
         /// </summary>
-        public ICalculationStatus IterationResult
+        public IterationStatus IterationResult
         {
             [DebuggerStepThrough]
             get
             {
-                return (_iterator != null) ? _iterator.Status : DefaultStatus;
+                return (_iterator != null) ? _iterator.Status : IterationStatus.Indetermined;
             }
         }
 
@@ -735,7 +728,8 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers
                 return true;
             }
 
-            return !_iterator.DetermineStatus(iterationNumber, result, source, residuals).TerminatesCalculation;
+            var status = _iterator.DetermineStatus(iterationNumber, result, source, residuals);
+            return status == IterationStatus.Running || status == IterationStatus.Indetermined;
         }
 
         /// <summary>
diff --git a/src/Numerics/LinearAlgebra/Double/Solvers/StopCriterium/DivergenceStopCriterium.cs b/src/Numerics/LinearAlgebra/Double/Solvers/StopCriterium/DivergenceStopCriterium.cs
index b44cd30f..c5468f47 100644
--- a/src/Numerics/LinearAlgebra/Double/Solvers/StopCriterium/DivergenceStopCriterium.cs
+++ b/src/Numerics/LinearAlgebra/Double/Solvers/StopCriterium/DivergenceStopCriterium.cs
@@ -29,7 +29,6 @@
 // </copyright>
 
 using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using System;
 using System.Diagnostics;
 
@@ -58,11 +57,6 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers.StopCriterium
         /// </summary>
         private const int DefaultLastIterationNumber = -1;
 
-        /// <summary>
-        /// The default status.
-        /// </summary>
-        private static readonly ICalculationStatus DefaultStatus = new CalculationIndetermined();
-        
         /// <summary>
         /// The maximum relative increase the residual may experience without triggering a divergence warning.
         /// </summary>
@@ -76,7 +70,7 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers.StopCriterium
         /// <summary>
         /// The status of the calculation
         /// </summary>
-        private ICalculationStatus _status = DefaultStatus;
+        private IterationStatus _status = IterationStatus.Indetermined;
 
         /// <summary>
         /// The array that holds the tracking information.
@@ -217,18 +211,13 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers.StopCriterium
         /// on the invocation of this method. Therefore this method should only be called if the 
         /// calculation has moved forwards at least one step.
         /// </remarks>
-        public ICalculationStatus DetermineStatus(int iterationNumber, Vector<double> solutionVector, Vector<double> sourceVector, Vector<double> residualVector)
+        public IterationStatus DetermineStatus(int iterationNumber, Vector<double> solutionVector, Vector<double> sourceVector, Vector<double> residualVector)
         {
             if (iterationNumber < 0)
             {
                 throw new ArgumentOutOfRangeException("iterationNumber");
             }
 
-            if (residualVector == null)
-            {
-                throw new ArgumentNullException("residualVector");
-            }
-
             if (_lastIteration >= iterationNumber)
             {
                 // We have already stored the actual last iteration number
@@ -256,19 +245,12 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers.StopCriterium
             // Stop the iteration.
             if (double.IsNaN(_residualHistory[_residualHistory.Length - 1]))
             {
-                SetStatusToDiverged();
+                _status = IterationStatus.Diverged;
                 return _status;
             }
 
             // Check if we are diverging and if so set the status
-            if (IsDiverging())
-            {
-                SetStatusToDiverged();
-            }
-            else
-            {
-                SetStatusToRunning();
-            }
+            _status = IsDiverging() ? IterationStatus.Diverged : IterationStatus.Running;
 
             _lastIteration = iterationNumber;
             return _status;
@@ -312,32 +294,10 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers.StopCriterium
             }
         }
 
-        /// <summary>
-        /// Set status to <see cref="CalculationDiverged"/>
-        /// </summary>
-        private void SetStatusToDiverged()
-        {
-            if (!(_status is CalculationDiverged))
-            {
-                _status = new CalculationDiverged();
-            }
-        }
-
-        /// <summary>
-        /// Set status to <see cref="CalculationRunning"/>
-        /// </summary>
-        private void SetStatusToRunning()
-        {
-            if (!(_status is CalculationRunning))
-            {
-                _status = new CalculationRunning();
-            }
-        }
-
         /// <summary>
         /// Gets the current calculation status.
         /// </summary>
-        public ICalculationStatus Status
+        public IterationStatus Status
         {
             [DebuggerStepThrough]
             get
@@ -351,7 +311,7 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers.StopCriterium
         /// </summary>
         public void ResetToPrecalculationState()
         {
-            _status = DefaultStatus;
+            _status = IterationStatus.Indetermined;
             _lastIteration = DefaultLastIterationNumber;
             _residualHistory = null;
         }
diff --git a/src/Numerics/LinearAlgebra/Double/Solvers/StopCriterium/FailureStopCriterium.cs b/src/Numerics/LinearAlgebra/Double/Solvers/StopCriterium/FailureStopCriterium.cs
index dd009098..7f561148 100644
--- a/src/Numerics/LinearAlgebra/Double/Solvers/StopCriterium/FailureStopCriterium.cs
+++ b/src/Numerics/LinearAlgebra/Double/Solvers/StopCriterium/FailureStopCriterium.cs
@@ -28,11 +28,10 @@
 // OTHER DEALINGS IN THE SOFTWARE.
 // </copyright>
 
-using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
-using MathNet.Numerics.Properties;
 using System;
 using System.Diagnostics;
+using MathNet.Numerics.LinearAlgebra.Solvers;
+using MathNet.Numerics.Properties;
 
 namespace MathNet.Numerics.LinearAlgebra.Double.Solvers.StopCriterium
 {
@@ -45,22 +44,17 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers.StopCriterium
         /// Defines the default last iteration number. Set to -1 because iterations normally
         /// start at 0.
         /// </summary>
-        private const int DefaultLastIterationNumber = -1;
-
-        /// <summary>
-        /// The default status.
-        /// </summary>
-        private static readonly ICalculationStatus DefaultStatus = new CalculationIndetermined();
+        const int DefaultLastIterationNumber = -1;
 
         /// <summary>
         /// The status of the calculation
         /// </summary>
-        private ICalculationStatus _status = DefaultStatus;
+        IterationStatus _status = IterationStatus.Indetermined;
 
         /// <summary>
         /// The iteration number of the last iteration.
         /// </summary>
-        private int _lastIteration = DefaultLastIterationNumber;
+        int _lastIteration = DefaultLastIterationNumber;
 
         /// <summary>
         /// Determines the status of the iterative calculation based on the stop criteria stored
@@ -75,23 +69,13 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers.StopCriterium
         /// on the invocation of this method. Therefore this method should only be called if the 
         /// calculation has moved forwards at least one step.
         /// </remarks>
-        public ICalculationStatus DetermineStatus(int iterationNumber, Vector<double> solutionVector, Vector<double> sourceVector, Vector<double> residualVector)
+        public IterationStatus DetermineStatus(int iterationNumber, Vector<double> solutionVector, Vector<double> sourceVector, Vector<double> residualVector)
         {
             if (iterationNumber < 0)
             {
                 throw new ArgumentOutOfRangeException("iterationNumber");
             }
 
-            if (solutionVector == null)
-            {
-                throw new ArgumentNullException("solutionVector");
-            }
-
-            if (residualVector == null)
-            {
-                throw new ArgumentNullException("residualVector");
-            }
-
             if (solutionVector.Count != residualVector.Count)
             {
                 throw new ArgumentException(Resources.ArgumentArraysSameLength);
@@ -108,45 +92,16 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers.StopCriterium
             var residualNorm = residualVector.InfinityNorm();
             var solutionNorm = solutionVector.InfinityNorm();
 
-            if (double.IsNaN(solutionNorm) || double.IsNaN(residualNorm))
-            {
-                SetStatusToFailed();
-            }
-            else
-            {
-                SetStatusToRunning();
-            }
+            _status = double.IsNaN(solutionNorm) || double.IsNaN(residualNorm) ? IterationStatus.Failure : IterationStatus.Running;
 
             _lastIteration = iterationNumber;
             return _status;
         }
 
-        /// <summary>
-        /// Set status to <see cref="CalculationFailure"/>
-        /// </summary>
-        private void SetStatusToFailed()
-        {
-            if (!(_status is CalculationFailure))
-            {
-                _status = new CalculationFailure();
-            }
-        }
-
-        /// <summary>
-        /// Set status to <see cref="CalculationRunning"/>
-        /// </summary>
-        private void SetStatusToRunning()
-        {
-            if (!(_status is CalculationRunning))
-            {
-                _status = new CalculationRunning();
-            }
-        }
-
         /// <summary>
         /// Gets the current calculation status.
         /// </summary>
-        public ICalculationStatus Status
+        public IterationStatus Status
         {
             [DebuggerStepThrough]
             get
@@ -160,7 +115,7 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers.StopCriterium
         /// </summary>
         public void ResetToPrecalculationState()
         {
-            _status = DefaultStatus;
+            _status = IterationStatus.Indetermined;
             _lastIteration = DefaultLastIterationNumber;
         }
 
diff --git a/src/Numerics/LinearAlgebra/Double/Solvers/StopCriterium/ResidualStopCriterium.cs b/src/Numerics/LinearAlgebra/Double/Solvers/StopCriterium/ResidualStopCriterium.cs
index 42d8a68e..f4246483 100644
--- a/src/Numerics/LinearAlgebra/Double/Solvers/StopCriterium/ResidualStopCriterium.cs
+++ b/src/Numerics/LinearAlgebra/Double/Solvers/StopCriterium/ResidualStopCriterium.cs
@@ -28,11 +28,10 @@
 // OTHER DEALINGS IN THE SOFTWARE.
 // </copyright>
 
-using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
-using MathNet.Numerics.Properties;
 using System;
 using System.Diagnostics;
+using MathNet.Numerics.LinearAlgebra.Solvers;
+using MathNet.Numerics.Properties;
 
 namespace MathNet.Numerics.LinearAlgebra.Double.Solvers.StopCriterium
 {
@@ -54,38 +53,33 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers.StopCriterium
         /// <summary>
         /// Defines the default last iteration number. Set to -1 because iterations normally start at 0.
         /// </summary>
-        private const int DefaultLastIterationNumber = -1;
-
-        /// <summary>
-        /// The default status.
-        /// </summary>
-        private static readonly ICalculationStatus DefaultStatus = new CalculationIndetermined();
+        const int DefaultLastIterationNumber = -1;
 
         /// <summary>
         /// The maximum value for the residual below which the calculation is considered converged.
         /// </summary>
-        private double _maximum;
+        double _maximum;
 
         /// <summary>
         /// The minimum number of iterations for which the residual has to be below the maximum before
         /// the calculation is considered converged.
         /// </summary>
-        private int _minimumIterationsBelowMaximum;
+        int _minimumIterationsBelowMaximum;
 
         /// <summary>
         /// The status of the calculation
         /// </summary>
-        private ICalculationStatus _status = DefaultStatus;
+        IterationStatus _status = IterationStatus.Indetermined;
 
         /// <summary>
         /// The number of iterations since the residuals got below the maximum.
         /// </summary>
-        private int _iterationCount;
+        int _iterationCount;
 
         /// <summary>
         /// The iteration number of the last iteration.
         /// </summary>
-        private int _lastIteration = DefaultLastIterationNumber;
+        int _lastIteration = DefaultLastIterationNumber;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="ResidualStopCriterium"/> class with the default maximum 
@@ -222,28 +216,13 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers.StopCriterium
         /// on the invocation of this method. Therefore this method should only be called if the 
         /// calculation has moved forwards at least one step.
         /// </remarks>
-        public ICalculationStatus DetermineStatus(int iterationNumber, Vector<double> solutionVector, Vector<double> sourceVector, Vector<double> residualVector)
+        public IterationStatus DetermineStatus(int iterationNumber, Vector<double> solutionVector, Vector<double> sourceVector, Vector<double> residualVector)
         {
             if (iterationNumber < 0)
             {
                 throw new ArgumentOutOfRangeException("iterationNumber");
             }
 
-            if (solutionVector == null)
-            {
-                throw new ArgumentNullException("solutionVector");
-            }
-
-            if (sourceVector == null)
-            {
-                throw new ArgumentNullException("sourceVector");
-            }
-            
-            if (residualVector == null)
-            {
-                throw new ArgumentNullException("residualVector");
-            }
-
             if (solutionVector.Count != sourceVector.Count)
             {
                 throw new ArgumentException(Resources.ArgumentVectorsSameLength, "sourceVector");
@@ -258,7 +237,7 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers.StopCriterium
             // These values will be used to calculate the relative drop in residuals
             // later on.
             var residualNorm = residualVector.InfinityNorm();
-            
+
             // Check the residuals by calculating:
             // ||r_i|| <= stop_tol * ||b||
             var stopCriterium = ComputeStopCriterium(sourceVector.InfinityNorm());
@@ -269,7 +248,7 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers.StopCriterium
             if (double.IsNaN(stopCriterium) || double.IsNaN(residualNorm))
             {
                 _iterationCount = 0;
-                SetStatusToDiverged();
+                _status = IterationStatus.Diverged;
                 return _status;
             }
 
@@ -281,20 +260,13 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers.StopCriterium
                 if (_lastIteration <= iterationNumber)
                 {
                     _iterationCount = iterationNumber - _lastIteration;
-                    if (_iterationCount >= _minimumIterationsBelowMaximum)
-                    {
-                        SetStatusToConverged();
-                    }
-                    else
-                    {
-                        SetStatusToRunning();
-                    }
+                    _status = _iterationCount >= _minimumIterationsBelowMaximum ? IterationStatus.Converged : IterationStatus.Running;
                 }
             }
             else
             {
                 _iterationCount = 0;
-                SetStatusToRunning();
+                _status = IterationStatus.Running;
             }
 
             _lastIteration = iterationNumber;
@@ -306,7 +278,7 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers.StopCriterium
         /// </summary>
         /// <param name="solutionNorm">Solution vector norm</param>
         /// <returns>Criterium value</returns>
-        private double ComputeStopCriterium(double solutionNorm)
+        double ComputeStopCriterium(double solutionNorm)
         {
             // This is criterium 1 from Templates for the solution of linear systems.
             // The problem with this criterium is that it's not limiting enough. For now 
@@ -314,46 +286,13 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers.StopCriterium
             // return mMaximumResidual * (System.Math.Abs(mMatrixNorm) * System.Math.Abs(solutionNorm) + System.Math.Abs(mVectorNorm));
 
             // For now use criterium 2 from Templates for the solution of linear systems. See page 60.
-            return _maximum * Math.Abs(solutionNorm);
-        }
-
-        /// <summary>
-        /// Set status to <see cref="CalculationDiverged"/>
-        /// </summary>
-        private void SetStatusToDiverged()
-        {
-            if (!(_status is CalculationDiverged))
-            {
-                _status = new CalculationDiverged();
-            }
-        }
-
-        /// <summary>
-        /// Set status to <see cref="CalculationConverged"/>
-        /// </summary>
-        private void SetStatusToConverged()
-        {
-            if (!(_status is CalculationConverged))
-            {
-                _status = new CalculationConverged();
-            }
-        }
-
-        /// <summary>
-        /// Set status to <see cref="CalculationRunning"/>
-        /// </summary>
-        private void SetStatusToRunning()
-        {
-            if (!(_status is CalculationRunning))
-            {
-                _status = new CalculationRunning();
-            }
+            return _maximum*Math.Abs(solutionNorm);
         }
 
         /// <summary>
         /// Gets the current calculation status.
         /// </summary>
-        public ICalculationStatus Status
+        public IterationStatus Status
         {
             [DebuggerStepThrough]
             get
@@ -367,7 +306,7 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers.StopCriterium
         /// </summary>
         public void ResetToPrecalculationState()
         {
-            _status = DefaultStatus;
+            _status = IterationStatus.Indetermined;
             _iterationCount = 0;
             _lastIteration = DefaultLastIterationNumber;
         }
diff --git a/src/Numerics/LinearAlgebra/Double/Solvers/TFQMR.cs b/src/Numerics/LinearAlgebra/Double/Solvers/TFQMR.cs
index df93300d..b4f4023d 100644
--- a/src/Numerics/LinearAlgebra/Double/Solvers/TFQMR.cs
+++ b/src/Numerics/LinearAlgebra/Double/Solvers/TFQMR.cs
@@ -30,7 +30,6 @@
 
 using System;
 using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using MathNet.Numerics.Properties;
 
 namespace MathNet.Numerics.LinearAlgebra.Double.Solvers
@@ -54,12 +53,6 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers
     /// </remarks>
     public sealed class TFQMR : IIterativeSolver<double>
     {
-        /// <summary>
-        /// The status used if there is no status, i.e. the solver hasn't run yet and there is no
-        /// iterator.
-        /// </summary>
-        static readonly ICalculationStatus DefaultStatus = new CalculationIndetermined();
-
         /// <summary>
         /// The preconditioner that will be used. Can be set to <see langword="null" />, in which case the default
         /// pre-conditioner will be used.
@@ -168,11 +161,11 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers
         /// <summary>
         /// Gets the status of the iteration once the calculation is finished.
         /// </summary>
-        public ICalculationStatus IterationResult
+        public IterationStatus IterationResult
         {
             get
             {
-                return (_iterator != null) ? _iterator.Status : DefaultStatus;
+                return (_iterator != null) ? _iterator.Status : IterationStatus.Indetermined;
             }
         }
 
@@ -459,7 +452,8 @@ namespace MathNet.Numerics.LinearAlgebra.Double.Solvers
                 return true;
             }
 
-            return !_iterator.DetermineStatus(iterationNumber, result, source, residuals).TerminatesCalculation;
+            var status = _iterator.DetermineStatus(iterationNumber, result, source, residuals);
+            return status == IterationStatus.Running || status == IterationStatus.Indetermined;
         }
 
         /// <summary>
diff --git a/src/Numerics/LinearAlgebra/Single/Solvers/BiCgStab.cs b/src/Numerics/LinearAlgebra/Single/Solvers/BiCgStab.cs
index ea9cc357..bb0e7189 100644
--- a/src/Numerics/LinearAlgebra/Single/Solvers/BiCgStab.cs
+++ b/src/Numerics/LinearAlgebra/Single/Solvers/BiCgStab.cs
@@ -30,7 +30,6 @@
 
 using System;
 using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using MathNet.Numerics.Properties;
 
 namespace MathNet.Numerics.LinearAlgebra.Single.Solvers
@@ -66,12 +65,6 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers
     /// </remarks>
     public sealed class BiCgStab : IIterativeSolver<float>
     {
-        /// <summary>
-        /// The status used if there is no status, i.e. the solver hasn't run yet and there is no
-        /// iterator.
-        /// </summary>
-        static readonly ICalculationStatus DefaultStatus = new CalculationIndetermined();
-
         /// <summary>
         /// The preconditioner that will be used. Can be set to <see langword="null" />, in which case the default
         /// pre-conditioner will be used.
@@ -180,11 +173,11 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers
         /// <summary>
         /// Gets the status of the iteration once the calculation is finished.
         /// </summary>
-        public ICalculationStatus IterationResult
+        public IterationStatus IterationResult
         {
             get
             {
-                return (_iterator != null) ? _iterator.Status : DefaultStatus;
+                return (_iterator != null) ? _iterator.Status : IterationStatus.Indetermined;
             }
         }
 
@@ -465,7 +458,8 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers
                 return true;
             }
 
-            return !_iterator.DetermineStatus(iterationNumber, result, source, residuals).TerminatesCalculation;
+            var status = _iterator.DetermineStatus(iterationNumber, result, source, residuals);
+            return status == IterationStatus.Running || status == IterationStatus.Indetermined;
         }
 
         /// <summary>
diff --git a/src/Numerics/LinearAlgebra/Single/Solvers/CompositeSolver.cs b/src/Numerics/LinearAlgebra/Single/Solvers/CompositeSolver.cs
index 3d63e4df..d516faf5 100644
--- a/src/Numerics/LinearAlgebra/Single/Solvers/CompositeSolver.cs
+++ b/src/Numerics/LinearAlgebra/Single/Solvers/CompositeSolver.cs
@@ -34,7 +34,6 @@ using System.IO;
 using System.Linq;
 using System.Reflection;
 using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using MathNet.Numerics.Properties;
 
 namespace MathNet.Numerics.LinearAlgebra.Single.Solvers
@@ -86,16 +85,6 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers
 
         #endregion
 
-        /// <summary>
-        /// The default status used if the solver is not running.
-        /// </summary>
-        static readonly ICalculationStatus NonRunningStatus = new CalculationIndetermined();
-
-        /// <summary>
-        /// The default status used if the solver is running.
-        /// </summary>
-        static readonly ICalculationStatus RunningStatus = new CalculationRunning();
-
 #if PORTABLE
         private static readonly Dictionary<double, List<IIterativeSolverSetup<float>>> SolverSetups = new Dictionary<double, List<IIterativeSolverSetup<float>>>();        
 #else
@@ -340,7 +329,7 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers
         /// <summary>
         /// The status of the calculation.
         /// </summary>
-        ICalculationStatus _status = NonRunningStatus;
+        IterationStatus _status = IterationStatus.Indetermined;
 
         /// <summary>
         /// The iterator that is used to control the iteration process.
@@ -386,7 +375,7 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers
         /// <summary>
         /// Gets the status of the iteration once the calculation is finished.
         /// </summary>
-        public ICalculationStatus IterationResult
+        public IterationStatus IterationResult
         {
             get
             {
@@ -509,7 +498,7 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers
                     // Switch to the next preconditioner. 
                     // Reset the solution vector to the previous solution
                     input.CopyTo(internalInput);
-                    _status = RunningStatus;
+                    _status = IterationStatus.Running;
                     continue;
                 }
 
diff --git a/src/Numerics/LinearAlgebra/Single/Solvers/GpBiCg.cs b/src/Numerics/LinearAlgebra/Single/Solvers/GpBiCg.cs
index f81a7253..999f1a00 100644
--- a/src/Numerics/LinearAlgebra/Single/Solvers/GpBiCg.cs
+++ b/src/Numerics/LinearAlgebra/Single/Solvers/GpBiCg.cs
@@ -30,7 +30,6 @@
 
 using System;
 using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using MathNet.Numerics.Properties;
 
 namespace MathNet.Numerics.LinearAlgebra.Single.Solvers
@@ -64,12 +63,6 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers
     /// </remarks>
     public sealed class GpBiCg : IIterativeSolver<float>
     {
-        /// <summary>
-        /// The status used if there is no status, i.e. the solver hasn't run yet and there is no
-        /// iterator.
-        /// </summary>
-        static readonly ICalculationStatus DefaultStatus = new CalculationIndetermined();
-
         /// <summary>
         /// The preconditioner that will be used. Can be set to <c>null</c>, in which case the default
         /// pre-conditioner will be used.
@@ -229,9 +222,9 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers
         /// <summary>
         /// Gets the status of the iteration once the calculation is finished.
         /// </summary>
-        public ICalculationStatus IterationResult
+        public IterationStatus IterationResult
         {
-            get { return (_iterator != null) ? _iterator.Status : DefaultStatus; }
+            get { return (_iterator != null) ? _iterator.Status : IterationStatus.Indetermined; }
         }
 
         /// <summary>
@@ -551,7 +544,8 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers
                 return true;
             }
 
-            return !_iterator.DetermineStatus(iterationNumber, result, source, residuals).TerminatesCalculation;
+            var status = _iterator.DetermineStatus(iterationNumber, result, source, residuals);
+            return status == IterationStatus.Running || status == IterationStatus.Indetermined;
         }
 
         /// <summary>
diff --git a/src/Numerics/LinearAlgebra/Single/Solvers/MlkBiCgStab.cs b/src/Numerics/LinearAlgebra/Single/Solvers/MlkBiCgStab.cs
index d61b6ba7..b54f9cd7 100644
--- a/src/Numerics/LinearAlgebra/Single/Solvers/MlkBiCgStab.cs
+++ b/src/Numerics/LinearAlgebra/Single/Solvers/MlkBiCgStab.cs
@@ -33,7 +33,6 @@ using System.Collections.Generic;
 using System.Diagnostics;
 using MathNet.Numerics.Distributions;
 using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using MathNet.Numerics.Properties;
 
 namespace MathNet.Numerics.LinearAlgebra.Single.Solvers
@@ -68,12 +67,6 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers
         /// </summary>
         const int DefaultNumberOfStartingVectors = 50;
 
-        /// <summary>
-        /// The status used if there is no status, i.e. the solver hasn't run yet and there is no
-        /// iterator.
-        /// </summary>
-        static readonly ICalculationStatus DefaultStatus = new CalculationIndetermined();
-
         /// <summary>
         /// The preconditioner that will be used. Can be set to <see langword="null" />, in which case the default
         /// pre-conditioner will be used.
@@ -253,12 +246,12 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers
         /// <summary>
         /// Gets the status of the iteration once the calculation is finished.
         /// </summary>
-        public ICalculationStatus IterationResult
+        public IterationStatus IterationResult
         {
             [DebuggerStepThrough]
             get
             {
-                return (_iterator != null) ? _iterator.Status : DefaultStatus;
+                return (_iterator != null) ? _iterator.Status : IterationStatus.Indetermined;
             }
         }
 
@@ -738,7 +731,8 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers
                 return true;
             }
 
-            return !_iterator.DetermineStatus(iterationNumber, result, source, residuals).TerminatesCalculation;
+            var status = _iterator.DetermineStatus(iterationNumber, result, source, residuals);
+            return status == IterationStatus.Running || status == IterationStatus.Indetermined;
         }
 
         /// <summary>
diff --git a/src/Numerics/LinearAlgebra/Single/Solvers/StopCriterium/DivergenceStopCriterium.cs b/src/Numerics/LinearAlgebra/Single/Solvers/StopCriterium/DivergenceStopCriterium.cs
index 7307af6c..77ff444b 100644
--- a/src/Numerics/LinearAlgebra/Single/Solvers/StopCriterium/DivergenceStopCriterium.cs
+++ b/src/Numerics/LinearAlgebra/Single/Solvers/StopCriterium/DivergenceStopCriterium.cs
@@ -29,7 +29,6 @@
 // </copyright>
 
 using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using System;
 using System.Diagnostics;
 
@@ -58,11 +57,6 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers.StopCriterium
         /// </summary>
         private const int DefaultLastIterationNumber = -1;
 
-        /// <summary>
-        /// The default status.
-        /// </summary>
-        private static readonly ICalculationStatus DefaultStatus = new CalculationIndetermined();
-        
         /// <summary>
         /// The maximum relative increase the residual may experience without triggering a divergence warning.
         /// </summary>
@@ -76,7 +70,7 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers.StopCriterium
         /// <summary>
         /// The status of the calculation
         /// </summary>
-        private ICalculationStatus _status = DefaultStatus;
+        private IterationStatus _status = IterationStatus.Indetermined;
 
         /// <summary>
         /// The array that holds the tracking information.
@@ -217,18 +211,13 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers.StopCriterium
         /// on the invocation of this method. Therefore this method should only be called if the 
         /// calculation has moved forwards at least one step.
         /// </remarks>
-        public ICalculationStatus DetermineStatus(int iterationNumber, Vector<float> solutionVector, Vector<float> sourceVector, Vector<float> residualVector)
+        public IterationStatus DetermineStatus(int iterationNumber, Vector<float> solutionVector, Vector<float> sourceVector, Vector<float> residualVector)
         {
             if (iterationNumber < 0)
             {
                 throw new ArgumentOutOfRangeException("iterationNumber");
             }
 
-            if (residualVector == null)
-            {
-                throw new ArgumentNullException("residualVector");
-            }
-
             if (_lastIteration >= iterationNumber)
             {
                 // We have already stored the actual last iteration number
@@ -256,19 +245,12 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers.StopCriterium
             // Stop the iteration.
             if (double.IsNaN(_residualHistory[_residualHistory.Length - 1]))
             {
-                SetStatusToDiverged();
+                _status = IterationStatus.Diverged;
                 return _status;
             }
 
             // Check if we are diverging and if so set the status
-            if (IsDiverging())
-            {
-                SetStatusToDiverged();
-            }
-            else
-            {
-                SetStatusToRunning();
-            }
+            _status = IsDiverging() ? IterationStatus.Diverged : IterationStatus.Running;
 
             _lastIteration = iterationNumber;
             return _status;
@@ -312,32 +294,10 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers.StopCriterium
             }
         }
 
-        /// <summary>
-        /// Set status to <see cref="CalculationDiverged"/>
-        /// </summary>
-        private void SetStatusToDiverged()
-        {
-            if (!(_status is CalculationDiverged))
-            {
-                _status = new CalculationDiverged();
-            }
-        }
-
-        /// <summary>
-        /// Set status to <see cref="CalculationRunning"/>
-        /// </summary>
-        private void SetStatusToRunning()
-        {
-            if (!(_status is CalculationRunning))
-            {
-                _status = new CalculationRunning();
-            }
-        }
-
         /// <summary>
         /// Gets the current calculation status.
         /// </summary>
-        public ICalculationStatus Status
+        public IterationStatus Status
         {
             [DebuggerStepThrough]
             get
@@ -351,7 +311,7 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers.StopCriterium
         /// </summary>
         public void ResetToPrecalculationState()
         {
-            _status = DefaultStatus;
+            _status = IterationStatus.Indetermined;
             _lastIteration = DefaultLastIterationNumber;
             _residualHistory = null;
         }
diff --git a/src/Numerics/LinearAlgebra/Single/Solvers/StopCriterium/FailureStopCriterium.cs b/src/Numerics/LinearAlgebra/Single/Solvers/StopCriterium/FailureStopCriterium.cs
index 10e3ea86..614b7579 100644
--- a/src/Numerics/LinearAlgebra/Single/Solvers/StopCriterium/FailureStopCriterium.cs
+++ b/src/Numerics/LinearAlgebra/Single/Solvers/StopCriterium/FailureStopCriterium.cs
@@ -28,11 +28,10 @@
 // OTHER DEALINGS IN THE SOFTWARE.
 // </copyright>
 
-using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
-using MathNet.Numerics.Properties;
 using System;
 using System.Diagnostics;
+using MathNet.Numerics.LinearAlgebra.Solvers;
+using MathNet.Numerics.Properties;
 
 namespace MathNet.Numerics.LinearAlgebra.Single.Solvers.StopCriterium
 {
@@ -47,15 +46,10 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers.StopCriterium
         /// </summary>
         private const int DefaultLastIterationNumber = -1;
 
-        /// <summary>
-        /// The default status.
-        /// </summary>
-        private static readonly ICalculationStatus DefaultStatus = new CalculationIndetermined();
-
         /// <summary>
         /// The status of the calculation
         /// </summary>
-        private ICalculationStatus _status = DefaultStatus;
+        private IterationStatus _status = IterationStatus.Indetermined;
 
         /// <summary>
         /// The iteration number of the last iteration.
@@ -75,23 +69,13 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers.StopCriterium
         /// on the invocation of this method. Therefore this method should only be called if the 
         /// calculation has moved forwards at least one step.
         /// </remarks>
-        public ICalculationStatus DetermineStatus(int iterationNumber, Vector<float> solutionVector, Vector<float> sourceVector, Vector<float> residualVector)
+        public IterationStatus DetermineStatus(int iterationNumber, Vector<float> solutionVector, Vector<float> sourceVector, Vector<float> residualVector)
         {
             if (iterationNumber < 0)
             {
                 throw new ArgumentOutOfRangeException("iterationNumber");
             }
 
-            if (solutionVector == null)
-            {
-                throw new ArgumentNullException("solutionVector");
-            }
-
-            if (residualVector == null)
-            {
-                throw new ArgumentNullException("residualVector");
-            }
-
             if (solutionVector.Count != residualVector.Count)
             {
                 throw new ArgumentException(Resources.ArgumentArraysSameLength);
@@ -108,45 +92,16 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers.StopCriterium
             var residualNorm = residualVector.InfinityNorm();
             var solutionNorm = solutionVector.InfinityNorm();
 
-            if (float.IsNaN(solutionNorm) || float.IsNaN(residualNorm))
-            {
-                SetStatusToFailed();
-            }
-            else
-            {
-                SetStatusToRunning();
-            }
+            _status = float.IsNaN(solutionNorm) || float.IsNaN(residualNorm) ? IterationStatus.Failure : IterationStatus.Running;
 
             _lastIteration = iterationNumber;
             return _status;
         }
 
-        /// <summary>
-        /// Set status to <see cref="CalculationFailure"/>
-        /// </summary>
-        private void SetStatusToFailed()
-        {
-            if (!(_status is CalculationFailure))
-            {
-                _status = new CalculationFailure();
-            }
-        }
-
-        /// <summary>
-        /// Set status to <see cref="CalculationRunning"/>
-        /// </summary>
-        private void SetStatusToRunning()
-        {
-            if (!(_status is CalculationRunning))
-            {
-                _status = new CalculationRunning();
-            }
-        }
-
         /// <summary>
         /// Gets the current calculation status.
         /// </summary>
-        public ICalculationStatus Status
+        public IterationStatus Status
         {
             [DebuggerStepThrough]
             get
@@ -160,7 +115,7 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers.StopCriterium
         /// </summary>
         public void ResetToPrecalculationState()
         {
-            _status = DefaultStatus;
+            _status = IterationStatus.Indetermined;
             _lastIteration = DefaultLastIterationNumber;
         }
 
diff --git a/src/Numerics/LinearAlgebra/Single/Solvers/StopCriterium/ResidualStopCriterium.cs b/src/Numerics/LinearAlgebra/Single/Solvers/StopCriterium/ResidualStopCriterium.cs
index 3859a42a..c07e5b23 100644
--- a/src/Numerics/LinearAlgebra/Single/Solvers/StopCriterium/ResidualStopCriterium.cs
+++ b/src/Numerics/LinearAlgebra/Single/Solvers/StopCriterium/ResidualStopCriterium.cs
@@ -28,11 +28,10 @@
 // OTHER DEALINGS IN THE SOFTWARE.
 // </copyright>
 
-using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
-using MathNet.Numerics.Properties;
 using System;
 using System.Diagnostics;
+using MathNet.Numerics.LinearAlgebra.Solvers;
+using MathNet.Numerics.Properties;
 
 namespace MathNet.Numerics.LinearAlgebra.Single.Solvers.StopCriterium
 {
@@ -54,38 +53,33 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers.StopCriterium
         /// <summary>
         /// Defines the default last iteration number. Set to -1 because iterations normally start at 0.
         /// </summary>
-        private const int DefaultLastIterationNumber = -1;
-
-        /// <summary>
-        /// The default status.
-        /// </summary>
-        private static readonly ICalculationStatus DefaultStatus = new CalculationIndetermined();
+        const int DefaultLastIterationNumber = -1;
 
         /// <summary>
         /// The maximum value for the residual below which the calculation is considered converged.
         /// </summary>
-        private float _maximum;
+        float _maximum;
 
         /// <summary>
         /// The minimum number of iterations for which the residual has to be below the maximum before
         /// the calculation is considered converged.
         /// </summary>
-        private int _minimumIterationsBelowMaximum;
+        int _minimumIterationsBelowMaximum;
 
         /// <summary>
         /// The status of the calculation
         /// </summary>
-        private ICalculationStatus _status = DefaultStatus;
+        IterationStatus _status = IterationStatus.Indetermined;
 
         /// <summary>
         /// The number of iterations since the residuals got below the maximum.
         /// </summary>
-        private int _iterationCount;
+        int _iterationCount;
 
         /// <summary>
         /// The iteration number of the last iteration.
         /// </summary>
-        private int _lastIteration = DefaultLastIterationNumber;
+        int _lastIteration = DefaultLastIterationNumber;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="ResidualStopCriterium"/> class with the default maximum 
@@ -222,28 +216,13 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers.StopCriterium
         /// on the invocation of this method. Therefore this method should only be called if the 
         /// calculation has moved forwards at least one step.
         /// </remarks>
-        public ICalculationStatus DetermineStatus(int iterationNumber, Vector<float> solutionVector, Vector<float> sourceVector, Vector<float> residualVector)
+        public IterationStatus DetermineStatus(int iterationNumber, Vector<float> solutionVector, Vector<float> sourceVector, Vector<float> residualVector)
         {
             if (iterationNumber < 0)
             {
                 throw new ArgumentOutOfRangeException("iterationNumber");
             }
 
-            if (solutionVector == null)
-            {
-                throw new ArgumentNullException("solutionVector");
-            }
-
-            if (sourceVector == null)
-            {
-                throw new ArgumentNullException("sourceVector");
-            }
-            
-            if (residualVector == null)
-            {
-                throw new ArgumentNullException("residualVector");
-            }
-
             if (solutionVector.Count != sourceVector.Count)
             {
                 throw new ArgumentException(Resources.ArgumentVectorsSameLength, "sourceVector");
@@ -258,7 +237,7 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers.StopCriterium
             // These values will be used to calculate the relative drop in residuals
             // later on.
             var residualNorm = residualVector.InfinityNorm();
-            
+
             // Check the residuals by calculating:
             // ||r_i|| <= stop_tol * ||b||
             var stopCriterium = ComputeStopCriterium(sourceVector.InfinityNorm());
@@ -269,7 +248,7 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers.StopCriterium
             if (float.IsNaN(stopCriterium) || float.IsNaN(residualNorm))
             {
                 _iterationCount = 0;
-                SetStatusToDiverged();
+                _status = IterationStatus.Diverged;
                 return _status;
             }
 
@@ -281,20 +260,13 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers.StopCriterium
                 if (_lastIteration <= iterationNumber)
                 {
                     _iterationCount = iterationNumber - _lastIteration;
-                    if (_iterationCount >= _minimumIterationsBelowMaximum)
-                    {
-                        SetStatusToConverged();
-                    }
-                    else
-                    {
-                        SetStatusToRunning();
-                    }
+                    _status = _iterationCount >= _minimumIterationsBelowMaximum ? IterationStatus.Converged : IterationStatus.Running;
                 }
             }
             else
             {
                 _iterationCount = 0;
-                SetStatusToRunning();
+                _status = IterationStatus.Running;
             }
 
             _lastIteration = iterationNumber;
@@ -306,7 +278,7 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers.StopCriterium
         /// </summary>
         /// <param name="solutionNorm">Solution vector norm</param>
         /// <returns>Criterium value</returns>
-        private float ComputeStopCriterium(float solutionNorm)
+        float ComputeStopCriterium(float solutionNorm)
         {
             // This is criterium 1 from Templates for the solution of linear systems.
             // The problem with this criterium is that it's not limiting enough. For now 
@@ -314,46 +286,13 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers.StopCriterium
             // return mMaximumResidual * (System.Math.Abs(mMatrixNorm) * System.Math.Abs(solutionNorm) + System.Math.Abs(mVectorNorm));
 
             // For now use criterium 2 from Templates for the solution of linear systems. See page 60.
-            return _maximum * Math.Abs(solutionNorm);
-        }
-
-        /// <summary>
-        /// Set status to <see cref="CalculationDiverged"/>
-        /// </summary>
-        private void SetStatusToDiverged()
-        {
-            if (!(_status is CalculationDiverged))
-            {
-                _status = new CalculationDiverged();
-            }
-        }
-
-        /// <summary>
-        /// Set status to <see cref="CalculationConverged"/>
-        /// </summary>
-        private void SetStatusToConverged()
-        {
-            if (!(_status is CalculationConverged))
-            {
-                _status = new CalculationConverged();
-            }
-        }
-
-        /// <summary>
-        /// Set status to <see cref="CalculationRunning"/>
-        /// </summary>
-        private void SetStatusToRunning()
-        {
-            if (!(_status is CalculationRunning))
-            {
-                _status = new CalculationRunning();
-            }
+            return _maximum*Math.Abs(solutionNorm);
         }
 
         /// <summary>
         /// Gets the current calculation status.
         /// </summary>
-        public ICalculationStatus Status
+        public IterationStatus Status
         {
             [DebuggerStepThrough]
             get
@@ -367,7 +306,7 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers.StopCriterium
         /// </summary>
         public void ResetToPrecalculationState()
         {
-            _status = DefaultStatus;
+            _status = IterationStatus.Indetermined;
             _iterationCount = 0;
             _lastIteration = DefaultLastIterationNumber;
         }
diff --git a/src/Numerics/LinearAlgebra/Single/Solvers/TFQMR.cs b/src/Numerics/LinearAlgebra/Single/Solvers/TFQMR.cs
index aa54e494..4b45737f 100644
--- a/src/Numerics/LinearAlgebra/Single/Solvers/TFQMR.cs
+++ b/src/Numerics/LinearAlgebra/Single/Solvers/TFQMR.cs
@@ -30,7 +30,6 @@
 
 using System;
 using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using MathNet.Numerics.Properties;
 
 namespace MathNet.Numerics.LinearAlgebra.Single.Solvers
@@ -54,12 +53,6 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers
     /// </remarks>
     public sealed class TFQMR : IIterativeSolver<float>
     {
-        /// <summary>
-        /// The status used if there is no status, i.e. the solver hasn't run yet and there is no
-        /// iterator.
-        /// </summary>
-        static readonly ICalculationStatus DefaultStatus = new CalculationIndetermined();
-
         /// <summary>
         /// The preconditioner that will be used. Can be set to <see langword="null" />, in which case the default
         /// pre-conditioner will be used.
@@ -169,9 +162,9 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers
         /// <summary>
         /// Gets the status of the iteration once the calculation is finished.
         /// </summary>
-        public ICalculationStatus IterationResult
+        public IterationStatus IterationResult
         {
-            get { return (_iterator != null) ? _iterator.Status : DefaultStatus; }
+            get { return (_iterator != null) ? _iterator.Status : IterationStatus.Indetermined; }
         }
 
         /// <summary>
@@ -457,7 +450,8 @@ namespace MathNet.Numerics.LinearAlgebra.Single.Solvers
                 return true;
             }
 
-            return !_iterator.DetermineStatus(iterationNumber, result, source, residuals).TerminatesCalculation;
+            var status = _iterator.DetermineStatus(iterationNumber, result, source, residuals);
+            return status == IterationStatus.Running || status == IterationStatus.Indetermined;
         }
 
         /// <summary>
diff --git a/src/Numerics/LinearAlgebra/Solvers/IIterationStopCriterium.cs b/src/Numerics/LinearAlgebra/Solvers/IIterationStopCriterium.cs
index 24495194..d216220c 100644
--- a/src/Numerics/LinearAlgebra/Solvers/IIterationStopCriterium.cs
+++ b/src/Numerics/LinearAlgebra/Solvers/IIterationStopCriterium.cs
@@ -50,13 +50,13 @@ namespace MathNet.Numerics.LinearAlgebra.Solvers
         /// on the invocation of this method. Therefore this method should only be called if the 
         /// calculation has moved forwards at least one step.
         /// </remarks>
-        ICalculationStatus DetermineStatus(int iterationNumber, Vector<T> solutionVector, Vector<T> sourceVector, Vector<T> residualVector);
+        IterationStatus DetermineStatus(int iterationNumber, Vector<T> solutionVector, Vector<T> sourceVector, Vector<T> residualVector);
 
         /// <summary>
         /// Gets the current calculation status.
         /// </summary>
         /// <remarks><see langword="null" /> is not a legal value. Status should be set in <see cref="DetermineStatus"/> implementation.</remarks>
-        ICalculationStatus Status { get; }
+        IterationStatus Status { get; }
 
         /// <summary>
         /// Resets the IIterationStopCriterium to the pre-calculation state.
diff --git a/src/Numerics/LinearAlgebra/Solvers/IIterativeSolver.cs b/src/Numerics/LinearAlgebra/Solvers/IIterativeSolver.cs
index 147f53f0..4dab99a8 100644
--- a/src/Numerics/LinearAlgebra/Solvers/IIterativeSolver.cs
+++ b/src/Numerics/LinearAlgebra/Solvers/IIterativeSolver.cs
@@ -55,7 +55,7 @@ namespace MathNet.Numerics.LinearAlgebra.Solvers
         /// <summary>
         /// Gets the status of the iteration once the calculation is finished.
         /// </summary>
-        ICalculationStatus IterationResult { get; }
+        IterationStatus IterationResult { get; }
 
         /// <summary>
         /// Solves the matrix equation Ax = b, where A is the coefficient matrix, b is the
diff --git a/src/Numerics/LinearAlgebra/Solvers/IterationCountStopCriterium.cs b/src/Numerics/LinearAlgebra/Solvers/IterationCountStopCriterium.cs
index e7a5c781..de7bad30 100644
--- a/src/Numerics/LinearAlgebra/Solvers/IterationCountStopCriterium.cs
+++ b/src/Numerics/LinearAlgebra/Solvers/IterationCountStopCriterium.cs
@@ -30,7 +30,6 @@
 
 using System;
 using System.Diagnostics;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 
 namespace MathNet.Numerics.LinearAlgebra.Solvers
 {
@@ -46,11 +45,6 @@ namespace MathNet.Numerics.LinearAlgebra.Solvers
         /// </summary>
         public const int DefaultMaximumNumberOfIterations = 1000;
 
-        /// <summary>
-        /// The default status.
-        /// </summary>
-        static readonly ICalculationStatus DefaultStatus = new CalculationIndetermined();
-
         /// <summary>
         /// The maximum number of iterations the calculation is allowed to perform.
         /// </summary>
@@ -59,7 +53,7 @@ namespace MathNet.Numerics.LinearAlgebra.Solvers
         /// <summary>
         /// The status of the calculation
         /// </summary>
-        ICalculationStatus _status = DefaultStatus;
+        IterationStatus _status = IterationStatus.Indetermined;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="IterationCountStopCriterium{T}"/> class with the default maximum 
@@ -91,7 +85,10 @@ namespace MathNet.Numerics.LinearAlgebra.Solvers
         public int MaximumNumberOfIterations
         {
             [DebuggerStepThrough]
-            get { return _maximumNumberOfIterations; }
+            get
+            {
+                return _maximumNumberOfIterations;
+            }
 
             [DebuggerStepThrough]
             set
@@ -126,53 +123,28 @@ namespace MathNet.Numerics.LinearAlgebra.Solvers
         /// on the invocation of this method. Therefore this method should only be called if the 
         /// calculation has moved forwards at least one step.
         /// </remarks>
-        public ICalculationStatus DetermineStatus(int iterationNumber, Vector<T> solutionVector, Vector<T> sourceVector, Vector<T> residualVector)
+        public IterationStatus DetermineStatus(int iterationNumber, Vector<T> solutionVector, Vector<T> sourceVector, Vector<T> residualVector)
         {
             if (iterationNumber < 0)
             {
                 throw new ArgumentOutOfRangeException("iterationNumber");
             }
 
-            if (iterationNumber >= _maximumNumberOfIterations)
-            {
-                SetStatusToFinished();
-            }
-            else
-            {
-                SetStatusToRunning();
-            }
-            return _status;
-        }
-
-        /// <summary>
-        /// Set status to <see cref="CalculationFailure"/>
-        /// </summary>
-        void SetStatusToFinished()
-        {
-            if (!(_status is CalculationStoppedWithoutConvergence))
-            {
-                _status = new CalculationStoppedWithoutConvergence();
-            }
-        }
+            _status = iterationNumber >= _maximumNumberOfIterations ? IterationStatus.StoppedWithoutConvergence : IterationStatus.Running;
 
-        /// <summary>
-        /// Set status to <see cref="CalculationRunning"/>
-        /// </summary>
-        void SetStatusToRunning()
-        {
-            if (!(_status is CalculationRunning))
-            {
-                _status = new CalculationRunning();
-            }
+            return _status;
         }
 
         /// <summary>
         /// Gets the current calculation status.
         /// </summary>
-        public ICalculationStatus Status
+        public IterationStatus Status
         {
             [DebuggerStepThrough]
-            get { return _status; }
+            get
+            {
+                return _status;
+            }
         }
 
         /// <summary>
@@ -180,7 +152,7 @@ namespace MathNet.Numerics.LinearAlgebra.Solvers
         /// </summary>
         public void ResetToPrecalculationState()
         {
-            _status = DefaultStatus;
+            _status = IterationStatus.Indetermined;
         }
 
         /// <summary>
diff --git a/src/Numerics/LinearAlgebra/Solvers/ICalculationStatus.cs b/src/Numerics/LinearAlgebra/Solvers/IterationStatus.cs
similarity index 80%
rename from src/Numerics/LinearAlgebra/Solvers/ICalculationStatus.cs
rename to src/Numerics/LinearAlgebra/Solvers/IterationStatus.cs
index 4b103fb9..274b98f2 100644
--- a/src/Numerics/LinearAlgebra/Solvers/ICalculationStatus.cs
+++ b/src/Numerics/LinearAlgebra/Solvers/IterationStatus.cs
@@ -1,4 +1,4 @@
-// <copyright file="ICalculationStatus.cs" company="Math.NET">
+// <copyright file="IterationStatus.cs" company="Math.NET">
 // Math.NET Numerics, part of the Math.NET Project
 // http://numerics.mathdotnet.com
 // http://github.com/mathnet/mathnet-numerics
@@ -31,13 +31,16 @@
 namespace MathNet.Numerics.LinearAlgebra.Solvers
 {
     /// <summary>
-    /// Defines the base interface for calculation status objects.
+    /// Iterative Calculation Status
     /// </summary>
-    public interface ICalculationStatus
+    public enum IterationStatus
     {
-        /// <summary>
-        /// Gets a value indicating whether current status warrants stopping the calculation.
-        /// </summary>
-        bool TerminatesCalculation { get; }
+        Indetermined = 0,
+        Running,
+        Converged,
+        Diverged,
+        StoppedWithoutConvergence,
+        Cancelled,
+        Failure
     }
 }
diff --git a/src/Numerics/LinearAlgebra/Solvers/Iterator.cs b/src/Numerics/LinearAlgebra/Solvers/Iterator.cs
index 726109b2..1504dba7 100644
--- a/src/Numerics/LinearAlgebra/Solvers/Iterator.cs
+++ b/src/Numerics/LinearAlgebra/Solvers/Iterator.cs
@@ -31,7 +31,6 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using MathNet.Numerics.Properties;
 
 namespace MathNet.Numerics.LinearAlgebra.Solvers
@@ -50,7 +49,7 @@ namespace MathNet.Numerics.LinearAlgebra.Solvers
         /// <summary>
         /// The status of the iterator.
         /// </summary>
-        ICalculationStatus _status = new CalculationIndetermined();
+        IterationStatus _status = IterationStatus.Indetermined;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="Iterator{T}"/> class with the specified stop criteria.
@@ -79,7 +78,7 @@ namespace MathNet.Numerics.LinearAlgebra.Solvers
         /// <summary>
         /// Gets the current calculation status.
         /// </summary>
-        public ICalculationStatus Status
+        public IterationStatus Status
         {
             get { return _status; }
         }
@@ -89,7 +88,7 @@ namespace MathNet.Numerics.LinearAlgebra.Solvers
         /// </summary>
         public bool HasConverged
         {
-            get { return _status is CalculationConverged; }
+            get { return _status == IterationStatus.Converged; }
         }
 
         /// <summary>
@@ -97,7 +96,7 @@ namespace MathNet.Numerics.LinearAlgebra.Solvers
         /// </summary>
         public bool HasStoppedWithoutConvergence
         {
-            get { return _status is CalculationStoppedWithoutConvergence; }
+            get { return _status == IterationStatus.StoppedWithoutConvergence; }
         }
 
         /// <summary>
@@ -113,7 +112,7 @@ namespace MathNet.Numerics.LinearAlgebra.Solvers
         /// on the invocation of this method. Therefore this method should only be called if the 
         /// calculation has moved forwards at least one step.
         /// </remarks>
-        public ICalculationStatus DetermineStatus(int iterationNumber, Vector<T> solutionVector, Vector<T> sourceVector, Vector<T> residualVector)
+        public IterationStatus DetermineStatus(int iterationNumber, Vector<T> solutionVector, Vector<T> sourceVector, Vector<T> residualVector)
         {
             if (_stopCriteria.Count == 0)
             {
@@ -126,7 +125,7 @@ namespace MathNet.Numerics.LinearAlgebra.Solvers
             }
 
             // While we're cancelled we don't call on the stop-criteria.
-            if (_status is CalculationCancelled)
+            if (_status == IterationStatus.Cancelled)
             {
                 return _status;
             }
@@ -140,7 +139,7 @@ namespace MathNet.Numerics.LinearAlgebra.Solvers
                 // - Indetermined --> keep going
                 // Anything else:
                 // Stop looping and set that status
-                if ((status is CalculationRunning) || (status is CalculationIndetermined))
+                if ((status == IterationStatus.Running) || (status == IterationStatus.Indetermined))
                 {
                     continue;
                 }
@@ -151,10 +150,7 @@ namespace MathNet.Numerics.LinearAlgebra.Solvers
 
             // Got all the way through
             // So we're running because we had vectors passed to us.
-            if (!(_status is CalculationRunning))
-            {
-                _status = new CalculationRunning();
-            }
+            _status = IterationStatus.Running;
 
             return _status;
         }
@@ -167,7 +163,7 @@ namespace MathNet.Numerics.LinearAlgebra.Solvers
         /// </remarks>
         public void Cancel()
         {
-            _status = new CalculationCancelled();
+            _status = IterationStatus.Cancelled;
         }
 
         /// <summary>
@@ -175,10 +171,8 @@ namespace MathNet.Numerics.LinearAlgebra.Solvers
         /// </summary>
         public void Reset()
         {
-            // Reset the status.
-            _status = new CalculationIndetermined();
+            _status = IterationStatus.Indetermined;
 
-            // Reset the stop-criteria
             foreach (var stopCriterium in _stopCriteria)
             {
                 stopCriterium.ResetToPrecalculationState();
diff --git a/src/Numerics/LinearAlgebra/Solvers/Status/CalculationCancelled.cs b/src/Numerics/LinearAlgebra/Solvers/Status/CalculationCancelled.cs
deleted file mode 100644
index 13a9df33..00000000
--- a/src/Numerics/LinearAlgebra/Solvers/Status/CalculationCancelled.cs
+++ /dev/null
@@ -1,49 +0,0 @@
-// <copyright file="CalculationCancelled.cs" company="Math.NET">
-// Math.NET Numerics, part of the Math.NET Project
-// http://numerics.mathdotnet.com
-// http://github.com/mathnet/mathnet-numerics
-// http://mathnetnumerics.codeplex.com
-//
-// Copyright (c) 2009-2010 Math.NET
-//
-// Permission is hereby granted, free of charge, to any person
-// obtaining a copy of this software and associated documentation
-// files (the "Software"), to deal in the Software without
-// restriction, including without limitation the rights to use,
-// copy, modify, merge, publish, distribute, sublicense, and/or sell
-// copies of the Software, and to permit persons to whom the
-// Software is furnished to do so, subject to the following
-// conditions:
-//
-// The above copyright notice and this permission notice shall be
-// included in all copies or substantial portions of the Software.
-//
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
-// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
-// OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
-// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
-// HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
-// WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
-// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
-// OTHER DEALINGS IN THE SOFTWARE.
-// </copyright>
-
-namespace MathNet.Numerics.LinearAlgebra.Solvers.Status
-{
-    /// <summary>
-    /// Indicates that a calculation was cancelled by the user.
-    /// </summary>
-    public struct CalculationCancelled : ICalculationStatus
-    {
-        /// <summary>
-        /// Gets a value indicating whether current status warrants stopping the calculation.
-        /// </summary>
-        public bool TerminatesCalculation
-        {
-            get
-            {
-                return true;
-            }
-        }
-    }
-}
diff --git a/src/Numerics/LinearAlgebra/Solvers/Status/CalculationConverged.cs b/src/Numerics/LinearAlgebra/Solvers/Status/CalculationConverged.cs
deleted file mode 100644
index 0a2e9f6b..00000000
--- a/src/Numerics/LinearAlgebra/Solvers/Status/CalculationConverged.cs
+++ /dev/null
@@ -1,51 +0,0 @@
-// <copyright file="CalculationConverged.cs" company="Math.NET">
-// Math.NET Numerics, part of the Math.NET Project
-// http://numerics.mathdotnet.com
-// http://github.com/mathnet/mathnet-numerics
-// http://mathnetnumerics.codeplex.com
-//
-// Copyright (c) 2009-2010 Math.NET
-//
-// Permission is hereby granted, free of charge, to any person
-// obtaining a copy of this software and associated documentation
-// files (the "Software"), to deal in the Software without
-// restriction, including without limitation the rights to use,
-// copy, modify, merge, publish, distribute, sublicense, and/or sell
-// copies of the Software, and to permit persons to whom the
-// Software is furnished to do so, subject to the following
-// conditions:
-//
-// The above copyright notice and this permission notice shall be
-// included in all copies or substantial portions of the Software.
-//
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
-// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
-// OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
-// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
-// HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
-// WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
-// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
-// OTHER DEALINGS IN THE SOFTWARE.
-// </copyright>
-
-namespace MathNet.Numerics.LinearAlgebra.Solvers.Status
-{
-    /// <summary>
-    /// Indicates that a calculation has converged to the desired convergence levels.
-    /// </summary>
-    public struct CalculationConverged : ICalculationStatus
-    {
-        /// <summary>
-        /// Gets a value indicating whether current status warrants stopping the calculation.
-        /// </summary>
-        public bool TerminatesCalculation
-        {
-            get
-            {
-                return true;
-            }
-        }
-
-        // TODO: CalculationConverged: Should we put the achieved residuals and convergence levels on here?
-    }
-}
diff --git a/src/Numerics/LinearAlgebra/Solvers/Status/CalculationDiverged.cs b/src/Numerics/LinearAlgebra/Solvers/Status/CalculationDiverged.cs
deleted file mode 100644
index ff9f22d7..00000000
--- a/src/Numerics/LinearAlgebra/Solvers/Status/CalculationDiverged.cs
+++ /dev/null
@@ -1,51 +0,0 @@
-// <copyright file="CalculationDiverged.cs" company="Math.NET">
-// Math.NET Numerics, part of the Math.NET Project
-// http://numerics.mathdotnet.com
-// http://github.com/mathnet/mathnet-numerics
-// http://mathnetnumerics.codeplex.com
-//
-// Copyright (c) 2009-2010 Math.NET
-//
-// Permission is hereby granted, free of charge, to any person
-// obtaining a copy of this software and associated documentation
-// files (the "Software"), to deal in the Software without
-// restriction, including without limitation the rights to use,
-// copy, modify, merge, publish, distribute, sublicense, and/or sell
-// copies of the Software, and to permit persons to whom the
-// Software is furnished to do so, subject to the following
-// conditions:
-//
-// The above copyright notice and this permission notice shall be
-// included in all copies or substantial portions of the Software.
-//
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
-// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
-// OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
-// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
-// HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
-// WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
-// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
-// OTHER DEALINGS IN THE SOFTWARE.
-// </copyright>
-
-namespace MathNet.Numerics.LinearAlgebra.Solvers.Status
-{
-    /// <summary>
-    /// Indicates that the calculation diverged.
-    /// </summary>
-    public struct CalculationDiverged : ICalculationStatus
-    {
-        /// <summary>
-        /// Gets a value indicating whether current status warrants stopping the calculation.
-        /// </summary>
-        public bool TerminatesCalculation
-        {
-            get
-            {
-                return true;
-            }
-        }
-
-        // TODO: CalculationDiverged - Should we put the residuals on here?
-    }
-}
diff --git a/src/Numerics/LinearAlgebra/Solvers/Status/CalculationFailure.cs b/src/Numerics/LinearAlgebra/Solvers/Status/CalculationFailure.cs
deleted file mode 100644
index 7d85b420..00000000
--- a/src/Numerics/LinearAlgebra/Solvers/Status/CalculationFailure.cs
+++ /dev/null
@@ -1,51 +0,0 @@
-// <copyright file="CalculationFailure.cs" company="Math.NET">
-// Math.NET Numerics, part of the Math.NET Project
-// http://numerics.mathdotnet.com
-// http://github.com/mathnet/mathnet-numerics
-// http://mathnetnumerics.codeplex.com
-//
-// Copyright (c) 2009-2010 Math.NET
-//
-// Permission is hereby granted, free of charge, to any person
-// obtaining a copy of this software and associated documentation
-// files (the "Software"), to deal in the Software without
-// restriction, including without limitation the rights to use,
-// copy, modify, merge, publish, distribute, sublicense, and/or sell
-// copies of the Software, and to permit persons to whom the
-// Software is furnished to do so, subject to the following
-// conditions:
-//
-// The above copyright notice and this permission notice shall be
-// included in all copies or substantial portions of the Software.
-//
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
-// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
-// OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
-// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
-// HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
-// WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
-// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
-// OTHER DEALINGS IN THE SOFTWARE.
-// </copyright>
-
-namespace MathNet.Numerics.LinearAlgebra.Solvers.Status
-{
-    /// <summary>
-    /// Indicates that a calculation has failed for some reason.
-    /// </summary>
-    public struct CalculationFailure : ICalculationStatus
-    {
-        /// <summary>
-        /// Gets a value indicating whether current status warrants stopping the calculation.
-        /// </summary>
-        public bool TerminatesCalculation
-        {
-            get
-            {
-                return true;
-            }
-        }
-
-        // TODO: CalcuationFailure - Indicate why the calculation has failed?
-    }
-}
diff --git a/src/Numerics/LinearAlgebra/Solvers/Status/CalculationIndetermined.cs b/src/Numerics/LinearAlgebra/Solvers/Status/CalculationIndetermined.cs
deleted file mode 100644
index 9d98c671..00000000
--- a/src/Numerics/LinearAlgebra/Solvers/Status/CalculationIndetermined.cs
+++ /dev/null
@@ -1,49 +0,0 @@
-// <copyright file="CalculationIndetermined.cs" company="Math.NET">
-// Math.NET Numerics, part of the Math.NET Project
-// http://numerics.mathdotnet.com
-// http://github.com/mathnet/mathnet-numerics
-// http://mathnetnumerics.codeplex.com
-//
-// Copyright (c) 2009-2010 Math.NET
-//
-// Permission is hereby granted, free of charge, to any person
-// obtaining a copy of this software and associated documentation
-// files (the "Software"), to deal in the Software without
-// restriction, including without limitation the rights to use,
-// copy, modify, merge, publish, distribute, sublicense, and/or sell
-// copies of the Software, and to permit persons to whom the
-// Software is furnished to do so, subject to the following
-// conditions:
-//
-// The above copyright notice and this permission notice shall be
-// included in all copies or substantial portions of the Software.
-//
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
-// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
-// OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
-// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
-// HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
-// WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
-// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
-// OTHER DEALINGS IN THE SOFTWARE.
-// </copyright>
-
-namespace MathNet.Numerics.LinearAlgebra.Solvers.Status
-{
-    /// <summary>
-    /// Indicates that the state of the calculation is indetermined, not started or stopped.
-    /// </summary>
-    public struct CalculationIndetermined : ICalculationStatus
-    {
-        /// <summary>
-        /// Gets a value indicating whether current status warrants stopping the calculation.
-        /// </summary>
-        public bool TerminatesCalculation
-        {
-            get
-            {
-                return false;
-            }
-        }
-    }
-}
diff --git a/src/Numerics/LinearAlgebra/Solvers/Status/CalculationRunning.cs b/src/Numerics/LinearAlgebra/Solvers/Status/CalculationRunning.cs
deleted file mode 100644
index bb431efe..00000000
--- a/src/Numerics/LinearAlgebra/Solvers/Status/CalculationRunning.cs
+++ /dev/null
@@ -1,51 +0,0 @@
-// <copyright file="CalculationRunning.cs" company="Math.NET">
-// Math.NET Numerics, part of the Math.NET Project
-// http://numerics.mathdotnet.com
-// http://github.com/mathnet/mathnet-numerics
-// http://mathnetnumerics.codeplex.com
-//
-// Copyright (c) 2009-2010 Math.NET
-//
-// Permission is hereby granted, free of charge, to any person
-// obtaining a copy of this software and associated documentation
-// files (the "Software"), to deal in the Software without
-// restriction, including without limitation the rights to use,
-// copy, modify, merge, publish, distribute, sublicense, and/or sell
-// copies of the Software, and to permit persons to whom the
-// Software is furnished to do so, subject to the following
-// conditions:
-//
-// The above copyright notice and this permission notice shall be
-// included in all copies or substantial portions of the Software.
-//
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
-// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
-// OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
-// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
-// HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
-// WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
-// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
-// OTHER DEALINGS IN THE SOFTWARE.
-// </copyright>
-
-namespace MathNet.Numerics.LinearAlgebra.Solvers.Status
-{
-    /// <summary>
-    /// Indicates that the calculation is running and no results are yet known.
-    /// </summary>
-    public struct CalculationRunning : ICalculationStatus
-    {
-        /// <summary>
-        /// Gets a value indicating whether current status warrants stopping the calculation.
-        /// </summary>
-        public bool TerminatesCalculation
-        {
-            get 
-            { 
-                return false; 
-            }
-        }
-
-        // TODO: CalculationRunning - Get current residuals?
-    }
-}
diff --git a/src/Numerics/LinearAlgebra/Solvers/Status/CalculationStoppedWithoutConvergence.cs b/src/Numerics/LinearAlgebra/Solvers/Status/CalculationStoppedWithoutConvergence.cs
deleted file mode 100644
index 72029810..00000000
--- a/src/Numerics/LinearAlgebra/Solvers/Status/CalculationStoppedWithoutConvergence.cs
+++ /dev/null
@@ -1,52 +0,0 @@
-// <copyright file="CalculationStoppedWithoutConvergence.cs" company="Math.NET">
-// Math.NET Numerics, part of the Math.NET Project
-// http://numerics.mathdotnet.com
-// http://github.com/mathnet/mathnet-numerics
-// http://mathnetnumerics.codeplex.com
-//
-// Copyright (c) 2009-2010 Math.NET
-//
-// Permission is hereby granted, free of charge, to any person
-// obtaining a copy of this software and associated documentation
-// files (the "Software"), to deal in the Software without
-// restriction, including without limitation the rights to use,
-// copy, modify, merge, publish, distribute, sublicense, and/or sell
-// copies of the Software, and to permit persons to whom the
-// Software is furnished to do so, subject to the following
-// conditions:
-//
-// The above copyright notice and this permission notice shall be
-// included in all copies or substantial portions of the Software.
-//
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
-// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
-// OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
-// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
-// HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
-// WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
-// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
-// OTHER DEALINGS IN THE SOFTWARE.
-// </copyright>
-
-namespace MathNet.Numerics.LinearAlgebra.Solvers.Status
-{
-    /// <summary>
-    /// Indicates that the calculation has been stopped due to reaching the stopping
-    /// limits, but that convergence was not achieved.
-    /// </summary>
-    public struct CalculationStoppedWithoutConvergence : ICalculationStatus
-    {
-        /// <summary>
-        /// Gets a value indicating whether current status warrants stopping the calculation.
-        /// </summary>
-        public bool TerminatesCalculation
-        {
-            get
-            {
-                return true;
-            }
-        }
-
-        // TODO: Indicate which stopping limit was reached?
-    }
-}
diff --git a/src/Numerics/Numerics.csproj b/src/Numerics/Numerics.csproj
index 741235e7..4088295d 100644
--- a/src/Numerics/Numerics.csproj
+++ b/src/Numerics/Numerics.csproj
@@ -123,6 +123,7 @@
     <Compile Include="Distributions\Zipf.cs" />
     <Compile Include="LinearAlgebra\Builder.cs" />
     <Compile Include="LinearAlgebra\Matrix.Factorization.cs" />
+    <Compile Include="LinearAlgebra\Solvers\IterationStatus.cs" />
     <Compile Include="LinearAlgebra\Solvers\Iterator.cs" />
     <Compile Include="LinearAlgebra\Solvers\IterationCountStopCriterium.cs" />
     <Compile Include="Providers\LinearAlgebra\Acml\AcmlLinearAlgebraProvider.Complex.cs" />
@@ -345,14 +346,6 @@
       <SubType>Code</SubType>
     </Compile>
     <Compile Include="LinearAlgebra\Solvers\UnitPreconditioner.cs" />
-    <Compile Include="LinearAlgebra\Solvers\Status\CalculationCancelled.cs" />
-    <Compile Include="LinearAlgebra\Solvers\Status\CalculationConverged.cs" />
-    <Compile Include="LinearAlgebra\Solvers\Status\CalculationDiverged.cs" />
-    <Compile Include="LinearAlgebra\Solvers\Status\CalculationFailure.cs" />
-    <Compile Include="LinearAlgebra\Solvers\Status\CalculationIndetermined.cs" />
-    <Compile Include="LinearAlgebra\Solvers\Status\CalculationRunning.cs" />
-    <Compile Include="LinearAlgebra\Solvers\Status\CalculationStoppedWithoutConvergence.cs" />
-    <Compile Include="LinearAlgebra\Solvers\ICalculationStatus.cs" />
     <Compile Include="LinearAlgebra\Double\Solvers\StopCriterium\DivergenceStopCriterium.cs" />
     <Compile Include="LinearAlgebra\Double\Solvers\StopCriterium\FailureStopCriterium.cs" />
     <Compile Include="LinearAlgebra\Double\Solvers\StopCriterium\ResidualStopCriterium.cs" />
diff --git a/src/UnitTests/LinearAlgebraTests/Complex/Solvers/IteratorTest.cs b/src/UnitTests/LinearAlgebraTests/Complex/Solvers/IteratorTest.cs
index 576064b6..ae7e5358 100644
--- a/src/UnitTests/LinearAlgebraTests/Complex/Solvers/IteratorTest.cs
+++ b/src/UnitTests/LinearAlgebraTests/Complex/Solvers/IteratorTest.cs
@@ -33,7 +33,6 @@ using System.Collections.Generic;
 using MathNet.Numerics.LinearAlgebra.Complex;
 using MathNet.Numerics.LinearAlgebra.Complex.Solvers.StopCriterium;
 using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using NUnit.Framework;
 
 namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex.Solvers
@@ -82,72 +81,6 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex.Solvers
                 DenseVector.Create(3, i => 6)));
         }
 
-        /// <summary>
-        /// Determine status with <c>null</c> solution vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullSolutionVectorThrowsArgumentNullException()
-        {
-            var criteria = new List<IIterationStopCriterium<Complex>>
-                {
-                    new FailureStopCriterium(),
-                    new DivergenceStopCriterium(),
-                    new IterationCountStopCriterium<Complex>(),
-                    new ResidualStopCriterium()
-                };
-            var iterator = new Iterator<Complex>(criteria);
-
-            Assert.Throws<ArgumentNullException>(() => iterator.DetermineStatus(
-                1,
-                null,
-                DenseVector.Create(3, i => 5),
-                DenseVector.Create(3, i => 6)));
-        }
-
-        /// <summary>
-        /// Determine status with <c>null</c> source vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullSourceVectorThrowsArgumentNullException()
-        {
-            var criteria = new List<IIterationStopCriterium<Complex>>
-                {
-                    new FailureStopCriterium(),
-                    new DivergenceStopCriterium(),
-                    new IterationCountStopCriterium<Complex>(),
-                    new ResidualStopCriterium()
-                };
-            var iterator = new Iterator<Complex>(criteria);
-
-            Assert.Throws<ArgumentNullException>(() => iterator.DetermineStatus(
-                1,
-                DenseVector.Create(3, i => 5),
-                null,
-                DenseVector.Create(3, i => 6)));
-        }
-
-        /// <summary>
-        /// Determine status with <c>null</c> residual vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullResidualVectorThrowsArgumentNullException()
-        {
-            var criteria = new List<IIterationStopCriterium<Complex>>
-                {
-                    new FailureStopCriterium(),
-                    new DivergenceStopCriterium(),
-                    new IterationCountStopCriterium<Complex>(),
-                    new ResidualStopCriterium()
-                };
-            var iterator = new Iterator<Complex>(criteria);
-
-            Assert.Throws<ArgumentNullException>(() => iterator.DetermineStatus(
-                1,
-                DenseVector.Create(3, i => 4),
-                DenseVector.Create(3, i => 5),
-                null));
-        }
-
         /// <summary>
         /// Can determine status.
         /// </summary>
@@ -169,7 +102,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex.Solvers
                 DenseVector.Create(3, i => 4),
                 DenseVector.Create(3, i => 4),
                 DenseVector.Create(3, i => 4));
-            Assert.IsInstanceOf(typeof (CalculationRunning), iterator.Status, "Incorrect status");
+            Assert.AreEqual(IterationStatus.Running, iterator.Status, "Incorrect status");
 
             // Second step, should run out of iterations.
             iterator.DetermineStatus(
@@ -177,7 +110,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex.Solvers
                 DenseVector.Create(3, i => 4),
                 DenseVector.Create(3, i => 4),
                 DenseVector.Create(3, i => 4));
-            Assert.IsInstanceOf(typeof (CalculationStoppedWithoutConvergence), iterator.Status, "Incorrect status");
+            Assert.AreEqual(IterationStatus.StoppedWithoutConvergence, iterator.Status, "Incorrect status");
         }
 
         /// <summary>
@@ -201,13 +134,13 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex.Solvers
                 DenseVector.Create(3, i => 4),
                 DenseVector.Create(3, i => 4),
                 DenseVector.Create(3, i => 4));
-            Assert.IsInstanceOf(typeof (CalculationRunning), iterator.Status, "Incorrect status");
+            Assert.AreEqual(IterationStatus.Running, iterator.Status, "Incorrect status");
 
             iterator.Reset();
-            Assert.IsInstanceOf(typeof (CalculationIndetermined), iterator.Status, "Incorrect status");
-            Assert.IsInstanceOf(typeof (CalculationIndetermined), criteria[0].Status, "Incorrect status");
-            Assert.IsInstanceOf(typeof (CalculationIndetermined), criteria[1].Status, "Incorrect status");
-            Assert.IsInstanceOf(typeof (CalculationIndetermined), criteria[2].Status, "Incorrect status");
+            Assert.AreEqual(IterationStatus.Indetermined, iterator.Status, "Incorrect status");
+            Assert.AreEqual(IterationStatus.Indetermined, criteria[0].Status, "Incorrect status");
+            Assert.AreEqual(IterationStatus.Indetermined, criteria[1].Status, "Incorrect status");
+            Assert.AreEqual(IterationStatus.Indetermined, criteria[2].Status, "Incorrect status");
         }
     }
 }
diff --git a/src/UnitTests/LinearAlgebraTests/Complex/Solvers/StopCriterium/DivergenceStopCriteriumTest.cs b/src/UnitTests/LinearAlgebraTests/Complex/Solvers/StopCriterium/DivergenceStopCriteriumTest.cs
index 5b81b2d0..85d95ca6 100644
--- a/src/UnitTests/LinearAlgebraTests/Complex/Solvers/StopCriterium/DivergenceStopCriteriumTest.cs
+++ b/src/UnitTests/LinearAlgebraTests/Complex/Solvers/StopCriterium/DivergenceStopCriteriumTest.cs
@@ -28,11 +28,11 @@
 // OTHER DEALINGS IN THE SOFTWARE.
 // </copyright>
 
+using System;
 using MathNet.Numerics.LinearAlgebra.Complex;
 using MathNet.Numerics.LinearAlgebra.Complex.Solvers.StopCriterium;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
+using MathNet.Numerics.LinearAlgebra.Solvers;
 using NUnit.Framework;
-using System;
 
 namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex.Solvers.StopCriterium
 {
@@ -119,20 +119,6 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex.Solvers.StopCrit
                 DenseVector.Create(3, i => 6)));
         }
 
-        /// <summary>
-        /// Determine status with <c>null</c> residual vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullResidualVectorThrowsArgumentNullException()
-        {
-            var criterium = new DivergenceStopCriterium(0.5, 15);
-            Assert.Throws<ArgumentNullException>(() => criterium.DetermineStatus(
-                1,
-                DenseVector.Create(3, i => 4),
-                DenseVector.Create(3, i => 5),
-                null));
-        }
-
         /// <summary>
         /// Can determine status with too few iterations.
         /// </summary>
@@ -153,7 +139,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex.Solvers.StopCrit
                     new DenseVector(new[] {new Complex(1.0, 0)}),
                     new DenseVector(new[] {new Complex((i + 1)*(Increase + 0.1), 0)}));
 
-                Assert.IsInstanceOf(typeof (CalculationRunning), status, "Status check fail.");
+                Assert.AreEqual(IterationStatus.Running, status, "Status check fail.");
             }
         }
 
@@ -177,7 +163,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex.Solvers.StopCrit
                     new DenseVector(new[] {new Complex(1.0, 0)}),
                     new DenseVector(new[] {new Complex((i + 1)*(Increase - 0.01), 0)}));
 
-                Assert.IsInstanceOf(typeof (CalculationRunning), status, "Status check fail.");
+                Assert.AreEqual(IterationStatus.Running, status, "Status check fail.");
             }
         }
 
@@ -201,7 +187,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex.Solvers.StopCrit
                     new DenseVector(new[] {new Complex(1.0, 0)}),
                     new DenseVector(new[] {new Complex((i + 1)*(Increase - 0.01), 0)}));
 
-                Assert.IsInstanceOf(typeof (CalculationRunning), status, "Status check fail.");
+                Assert.AreEqual(IterationStatus.Running, status, "Status check fail.");
             }
 
             // Now make it fail by throwing in a NaN
@@ -211,7 +197,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex.Solvers.StopCrit
                 new DenseVector(new[] {new Complex(1.0, 0)}),
                 new DenseVector(new[] {new Complex(double.NaN, 0)}));
 
-            Assert.IsInstanceOf(typeof (CalculationDiverged), status2, "Status check fail.");
+            Assert.AreEqual(IterationStatus.Diverged, status2, "Status check fail.");
         }
 
         /// <summary>
@@ -236,7 +222,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex.Solvers.StopCrit
                     new DenseVector(new[] {new Complex(1.0, 0)}),
                     new DenseVector(new[] {new Complex(previous, 0)}));
 
-                Assert.IsInstanceOf(typeof (CalculationRunning), status, "Status check fail.");
+                Assert.AreEqual(IterationStatus.Running, status, "Status check fail.");
             }
 
             // Add the final residual. Now we should have divergence
@@ -247,7 +233,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex.Solvers.StopCrit
                 new DenseVector(new[] {new Complex(1.0, 0)}),
                 new DenseVector(new[] {new Complex(previous, 0)}));
 
-            Assert.IsInstanceOf(typeof (CalculationDiverged), status2, "Status check fail.");
+            Assert.AreEqual(IterationStatus.Diverged, status2, "Status check fail.");
         }
 
         /// <summary>
@@ -268,14 +254,14 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex.Solvers.StopCrit
                 new DenseVector(new[] {new Complex(1.0, 0)}),
                 new DenseVector(new[] {new Complex(double.NaN, 0)}));
 
-            Assert.IsInstanceOf(typeof (CalculationDiverged), status, "Status check fail.");
+            Assert.AreEqual(IterationStatus.Diverged, status, "Status check fail.");
 
             // Reset the state
             criterium.ResetToPrecalculationState();
 
             Assert.AreEqual(Increase, criterium.MaximumRelativeIncrease, "Incorrect maximum");
             Assert.AreEqual(Iterations, criterium.MinimumNumberOfIterations, "Incorrect iteration count");
-            Assert.IsInstanceOf(typeof (CalculationIndetermined), criterium.Status, "Status check fail.");
+            Assert.AreEqual(IterationStatus.Indetermined, criterium.Status, "Status check fail.");
         }
 
         /// <summary>
diff --git a/src/UnitTests/LinearAlgebraTests/Complex/Solvers/StopCriterium/FailureStopCriteriumTest.cs b/src/UnitTests/LinearAlgebraTests/Complex/Solvers/StopCriterium/FailureStopCriteriumTest.cs
index 0b200356..e0639912 100644
--- a/src/UnitTests/LinearAlgebraTests/Complex/Solvers/StopCriterium/FailureStopCriteriumTest.cs
+++ b/src/UnitTests/LinearAlgebraTests/Complex/Solvers/StopCriterium/FailureStopCriteriumTest.cs
@@ -28,10 +28,10 @@
 // OTHER DEALINGS IN THE SOFTWARE.
 // </copyright>
 
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using System;
 using MathNet.Numerics.LinearAlgebra.Complex;
 using MathNet.Numerics.LinearAlgebra.Complex.Solvers.StopCriterium;
+using MathNet.Numerics.LinearAlgebra.Solvers;
 using NUnit.Framework;
 
 namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex.Solvers.StopCriterium
@@ -66,30 +66,6 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex.Solvers.StopCrit
             Assert.Throws<ArgumentOutOfRangeException>(() => criterium.DetermineStatus(-1, DenseVector.Create(3, i => 4), DenseVector.Create(3, i => 5), DenseVector.Create(3, i => 6)));
         }
 
-        /// <summary>
-        /// Determine status with <c>null</c> solution vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullSolutionVectorThrowsArgumentNullException()
-        {
-            var criterium = new FailureStopCriterium();
-            Assert.IsNotNull(criterium, "There should be a criterium");
-
-            Assert.Throws<ArgumentNullException>(() => criterium.DetermineStatus(1, null, DenseVector.Create(3, i => 6), DenseVector.Create(4, i => 4)));
-        }
-
-        /// <summary>
-        /// Determine status with <c>null</c> residual vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullResidualVectorThrowsArgumentNullException()
-        {
-            var criterium = new FailureStopCriterium();
-            Assert.IsNotNull(criterium, "There should be a criterium");
-
-            Assert.Throws<ArgumentNullException>(() => criterium.DetermineStatus(1, DenseVector.Create(3, i => 4), DenseVector.Create(3, i => 6), null));
-        }
-
         /// <summary>
         /// Determine status with non-matching vectors throws <c>ArgumentException</c>.
         /// </summary>
@@ -116,7 +92,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex.Solvers.StopCrit
             var residual = new DenseVector(new[] {new Complex(1000, 0), new Complex(double.NaN, 0), new Complex(2001, 0)});
 
             var status = criterium.DetermineStatus(5, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationFailure), status, "Should be failed");
+            Assert.AreEqual(IterationStatus.Failure, status, "Should be failed");
         }
 
         /// <summary>
@@ -133,7 +109,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex.Solvers.StopCrit
             var residual = new DenseVector(new[] {new Complex(1000, 0), new Complex(1000, 0), new Complex(2001, 0)});
 
             var status = criterium.DetermineStatus(5, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationFailure), status, "Should be failed");
+            Assert.AreEqual(IterationStatus.Failure, status, "Should be failed");
         }
 
         /// <summary>
@@ -150,7 +126,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex.Solvers.StopCrit
             var residual = new DenseVector(new[] {new Complex(1.0, 0), new Complex(2.0, 0), new Complex(3, 0)});
 
             var status = criterium.DetermineStatus(5, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationRunning), status, "Should be running");
+            Assert.AreEqual(IterationStatus.Running, status, "Should be running");
         }
 
         /// <summary>
@@ -167,10 +143,10 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex.Solvers.StopCrit
             var residual = new DenseVector(new[] {new Complex(1000, 0), new Complex(1000, 0), new Complex(2001, 0)});
 
             var status = criterium.DetermineStatus(5, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationRunning), status, "Should be running");
+            Assert.AreEqual(IterationStatus.Running, status, "Should be running");
 
             criterium.ResetToPrecalculationState();
-            Assert.IsInstanceOf(typeof (CalculationIndetermined), criterium.Status, "Should not have started");
+            Assert.AreEqual(IterationStatus.Indetermined, criterium.Status, "Should not have started");
         }
 
         /// <summary>
diff --git a/src/UnitTests/LinearAlgebraTests/Complex/Solvers/StopCriterium/IterationCountStopCriteriumTest.cs b/src/UnitTests/LinearAlgebraTests/Complex/Solvers/StopCriterium/IterationCountStopCriteriumTest.cs
index bd7dd0f7..39fcc962 100644
--- a/src/UnitTests/LinearAlgebraTests/Complex/Solvers/StopCriterium/IterationCountStopCriteriumTest.cs
+++ b/src/UnitTests/LinearAlgebraTests/Complex/Solvers/StopCriterium/IterationCountStopCriteriumTest.cs
@@ -31,7 +31,6 @@
 using System;
 using MathNet.Numerics.LinearAlgebra.Complex;
 using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using NUnit.Framework;
 
 namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex.Solvers.StopCriterium
@@ -100,10 +99,10 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex.Solvers.StopCrit
             Assert.IsNotNull(criterium, "A criterium should have been created");
 
             var status = criterium.DetermineStatus(5, DenseVector.Create(3, i => 1), DenseVector.Create(3, i => 2), DenseVector.Create(3, i => 3));
-            Assert.IsInstanceOf(typeof (CalculationRunning), status, "Should be running");
+            Assert.AreEqual(IterationStatus.Running, status, "Should be running");
 
             var status2 = criterium.DetermineStatus(10, DenseVector.Create(3, i => 1), DenseVector.Create(3, i => 2), DenseVector.Create(3, i => 3));
-            Assert.IsInstanceOf(typeof (CalculationStoppedWithoutConvergence), status2, "Should be finished");
+            Assert.AreEqual(IterationStatus.StoppedWithoutConvergence, status2, "Should be finished");
         }
 
         /// <summary>
@@ -116,10 +115,10 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex.Solvers.StopCrit
             Assert.IsNotNull(criterium, "A criterium should have been created");
 
             var status = criterium.DetermineStatus(5, DenseVector.Create(3, i => 1), DenseVector.Create(3, i => 2), DenseVector.Create(3, i => 3));
-            Assert.IsInstanceOf(typeof (CalculationRunning), status, "Should be running");
+            Assert.AreEqual(IterationStatus.Running, status, "Should be running");
 
             criterium.ResetToPrecalculationState();
-            Assert.IsInstanceOf(typeof (CalculationIndetermined), criterium.Status, "Should not have started");
+            Assert.AreEqual(IterationStatus.Indetermined, criterium.Status, "Should not have started");
         }
 
         /// <summary>
diff --git a/src/UnitTests/LinearAlgebraTests/Complex/Solvers/StopCriterium/ResidualStopCriteriumTest.cs b/src/UnitTests/LinearAlgebraTests/Complex/Solvers/StopCriterium/ResidualStopCriteriumTest.cs
index fef7fd3e..bff3d30e 100644
--- a/src/UnitTests/LinearAlgebraTests/Complex/Solvers/StopCriterium/ResidualStopCriteriumTest.cs
+++ b/src/UnitTests/LinearAlgebraTests/Complex/Solvers/StopCriterium/ResidualStopCriteriumTest.cs
@@ -28,11 +28,11 @@
 // OTHER DEALINGS IN THE SOFTWARE.
 // </copyright>
 
+using System;
 using MathNet.Numerics.LinearAlgebra.Complex;
 using MathNet.Numerics.LinearAlgebra.Complex.Solvers.StopCriterium;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
+using MathNet.Numerics.LinearAlgebra.Solvers;
 using NUnit.Framework;
-using System;
 
 namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex.Solvers.StopCriterium
 {
@@ -117,54 +117,6 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex.Solvers.StopCrit
                 DenseVector.Create(3, i => 6)));
         }
 
-        /// <summary>
-        /// Determine status with <c>null</c> solution vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullSolutionVectorThrowsArgumentNullException()
-        {
-            var criterium = new ResidualStopCriterium(1e-8, 50);
-            Assert.IsNotNull(criterium, "There should be a criterium");
-
-            Assert.Throws<ArgumentNullException>(() => criterium.DetermineStatus(
-                1,
-                null,
-                DenseVector.Create(3, i => 5),
-                DenseVector.Create(3, i => 6)));
-        }
-
-        /// <summary>
-        /// Determine status with <c>null</c> source vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullSourceVectorThrowsArgumentNullException()
-        {
-            var criterium = new ResidualStopCriterium(1e-8, 50);
-            Assert.IsNotNull(criterium, "There should be a criterium");
-
-            Assert.Throws<ArgumentNullException>(() => criterium.DetermineStatus(
-                1,
-                DenseVector.Create(3, i => 4),
-                null,
-                DenseVector.Create(3, i => 6)));
-        }
-
-        /// <summary>
-        /// Determine status with <c>null</c> residual vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullResidualVectorThrowsArgumentNullException()
-        {
-            var criterium = new ResidualStopCriterium(1e-8, 50);
-            Assert.IsNotNull(criterium, "There should be a criterium");
-
-            Assert.Throws<ArgumentNullException>(() => criterium.DetermineStatus(
-                1,
-                DenseVector.Create(3, i => 4),
-                DenseVector.Create(3, i => 5),
-                null));
-        }
-
         /// <summary>
         /// Determine status with non-matching solution vector throws <c>ArgumentException</c>.
         /// </summary>
@@ -227,7 +179,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex.Solvers.StopCrit
             var residual = new DenseVector(new[] {new Complex(1000.0, 1), new Complex(1000.0, 1), new Complex(2001.0, 1)});
 
             var status = criterium.DetermineStatus(5, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationDiverged), status, "Should be diverged");
+            Assert.AreEqual(IterationStatus.Diverged, status, "Should be diverged");
         }
 
         /// <summary>
@@ -244,7 +196,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex.Solvers.StopCrit
             var residual = new DenseVector(new[] {new Complex(1000.0, 1), new Complex(double.NaN, 1), new Complex(2001.0, 1)});
 
             var status = criterium.DetermineStatus(5, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationDiverged), status, "Should be diverged");
+            Assert.AreEqual(IterationStatus.Diverged, status, "Should be diverged");
         }
 
         /// <summary>
@@ -265,7 +217,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex.Solvers.StopCrit
             var residual = new DenseVector(new[] {Complex.Zero, Complex.Zero, Complex.Zero});
 
             var status = criterium.DetermineStatus(0, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationConverged), status, "Should be done");
+            Assert.AreEqual(IterationStatus.Converged, status, "Should be done");
         }
 
         /// <summary>
@@ -287,10 +239,10 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex.Solvers.StopCrit
             var residual = new DenseVector(new[] {new Complex(0.001, 0), new Complex(0.001, 0), new Complex(0.002, 0)});
 
             var status = criterium.DetermineStatus(5, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationRunning), status, "Should still be running");
+            Assert.AreEqual(IterationStatus.Running, status, "Should still be running");
 
             var status2 = criterium.DetermineStatus(16, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationConverged), status2, "Should be done");
+            Assert.AreEqual(IterationStatus.Converged, status2, "Should be done");
         }
 
         /// <summary>
@@ -307,10 +259,10 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex.Solvers.StopCrit
             var residual = new DenseVector(new[] {new Complex(1.000, 0), new Complex(1.000, 0), new Complex(2.001, 0)});
 
             var status = criterium.DetermineStatus(5, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationRunning), status, "Should be running");
+            Assert.AreEqual(IterationStatus.Running, status, "Should be running");
 
             criterium.ResetToPrecalculationState();
-            Assert.IsInstanceOf(typeof (CalculationIndetermined), criterium.Status, "Should not have started");
+            Assert.AreEqual(IterationStatus.Indetermined, criterium.Status, "Should not have started");
         }
 
         /// <summary>
diff --git a/src/UnitTests/LinearAlgebraTests/Complex32/Solvers/IteratorTest.cs b/src/UnitTests/LinearAlgebraTests/Complex32/Solvers/IteratorTest.cs
index 9dfaecfd..331d9b48 100644
--- a/src/UnitTests/LinearAlgebraTests/Complex32/Solvers/IteratorTest.cs
+++ b/src/UnitTests/LinearAlgebraTests/Complex32/Solvers/IteratorTest.cs
@@ -33,7 +33,6 @@ using System.Collections.Generic;
 using MathNet.Numerics.LinearAlgebra.Complex32;
 using MathNet.Numerics.LinearAlgebra.Complex32.Solvers.StopCriterium;
 using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using NUnit.Framework;
 
 namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex32.Solvers
@@ -82,72 +81,6 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex32.Solvers
                 DenseVector.Create(3, i => 6)));
         }
 
-        /// <summary>
-        /// Determine status with <c>null</c> solution vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullSolutionVectorThrowsArgumentNullException()
-        {
-            var criteria = new List<IIterationStopCriterium<Complex32>>
-                {
-                    new FailureStopCriterium(),
-                    new DivergenceStopCriterium(),
-                    new IterationCountStopCriterium<Complex32>(),
-                    new ResidualStopCriterium()
-                };
-            var iterator = new Iterator<Complex32>(criteria);
-
-            Assert.Throws<ArgumentNullException>(() => iterator.DetermineStatus(
-                1,
-                null,
-                DenseVector.Create(3, i => 5),
-                DenseVector.Create(3, i => 6)));
-        }
-
-        /// <summary>
-        /// Determine status with <c>null</c> source vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullSourceVectorThrowsArgumentNullException()
-        {
-            var criteria = new List<IIterationStopCriterium<Complex32>>
-                {
-                    new FailureStopCriterium(),
-                    new DivergenceStopCriterium(),
-                    new IterationCountStopCriterium<Complex32>(),
-                    new ResidualStopCriterium()
-                };
-            var iterator = new Iterator<Complex32>(criteria);
-
-            Assert.Throws<ArgumentNullException>(() => iterator.DetermineStatus(
-                1,
-                DenseVector.Create(3, i => 5),
-                null,
-                DenseVector.Create(3, i => 6)));
-        }
-
-        /// <summary>
-        /// Determine status with <c>null</c> residual vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullResidualVectorThrowsArgumentNullException()
-        {
-            var criteria = new List<IIterationStopCriterium<Complex32>>
-                {
-                    new FailureStopCriterium(),
-                    new DivergenceStopCriterium(),
-                    new IterationCountStopCriterium<Complex32>(),
-                    new ResidualStopCriterium()
-                };
-            var iterator = new Iterator<Complex32>(criteria);
-
-            Assert.Throws<ArgumentNullException>(() => iterator.DetermineStatus(
-                1,
-                DenseVector.Create(3, i => 4),
-                DenseVector.Create(3, i => 5),
-                null));
-        }
-
         /// <summary>
         /// Can determine status.
         /// </summary>
@@ -169,7 +102,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex32.Solvers
                 DenseVector.Create(3, i => 4),
                 DenseVector.Create(3, i => 4),
                 DenseVector.Create(3, i => 4));
-            Assert.IsInstanceOf(typeof (CalculationRunning), iterator.Status, "Incorrect status");
+            Assert.AreEqual(IterationStatus.Running, iterator.Status, "Incorrect status");
 
             // Second step, should run out of iterations.
             iterator.DetermineStatus(
@@ -177,7 +110,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex32.Solvers
                 DenseVector.Create(3, i => 4),
                 DenseVector.Create(3, i => 4),
                 DenseVector.Create(3, i => 4));
-            Assert.IsInstanceOf(typeof (CalculationStoppedWithoutConvergence), iterator.Status, "Incorrect status");
+            Assert.AreEqual(IterationStatus.StoppedWithoutConvergence, iterator.Status, "Incorrect status");
         }
 
         /// <summary>
@@ -201,13 +134,13 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex32.Solvers
                 DenseVector.Create(3, i => 4),
                 DenseVector.Create(3, i => 4),
                 DenseVector.Create(3, i => 4));
-            Assert.IsInstanceOf(typeof (CalculationRunning), iterator.Status, "Incorrect status");
+            Assert.AreEqual(IterationStatus.Running, iterator.Status, "Incorrect status");
 
             iterator.Reset();
-            Assert.IsInstanceOf(typeof (CalculationIndetermined), iterator.Status, "Incorrect status");
-            Assert.IsInstanceOf(typeof (CalculationIndetermined), criteria[0].Status, "Incorrect status");
-            Assert.IsInstanceOf(typeof (CalculationIndetermined), criteria[1].Status, "Incorrect status");
-            Assert.IsInstanceOf(typeof (CalculationIndetermined), criteria[2].Status, "Incorrect status");
+            Assert.AreEqual(IterationStatus.Indetermined, iterator.Status, "Incorrect status");
+            Assert.AreEqual(IterationStatus.Indetermined, criteria[0].Status, "Incorrect status");
+            Assert.AreEqual(IterationStatus.Indetermined, criteria[1].Status, "Incorrect status");
+            Assert.AreEqual(IterationStatus.Indetermined, criteria[2].Status, "Incorrect status");
         }
     }
 }
diff --git a/src/UnitTests/LinearAlgebraTests/Complex32/Solvers/StopCriterium/DivergenceStopCriteriumTest.cs b/src/UnitTests/LinearAlgebraTests/Complex32/Solvers/StopCriterium/DivergenceStopCriteriumTest.cs
index fd1a09f9..44c68367 100644
--- a/src/UnitTests/LinearAlgebraTests/Complex32/Solvers/StopCriterium/DivergenceStopCriteriumTest.cs
+++ b/src/UnitTests/LinearAlgebraTests/Complex32/Solvers/StopCriterium/DivergenceStopCriteriumTest.cs
@@ -28,11 +28,11 @@
 // OTHER DEALINGS IN THE SOFTWARE.
 // </copyright>
 
+using System;
 using MathNet.Numerics.LinearAlgebra.Complex32;
 using MathNet.Numerics.LinearAlgebra.Complex32.Solvers.StopCriterium;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
+using MathNet.Numerics.LinearAlgebra.Solvers;
 using NUnit.Framework;
-using System;
 
 namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex32.Solvers.StopCriterium
 {
@@ -119,20 +119,6 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex32.Solvers.StopCr
                 DenseVector.Create(3, i => 6)));
         }
 
-        /// <summary>
-        /// Determine status with <c>null</c> residual vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullResidualVectorThrowsArgumentNullException()
-        {
-            var criterium = new DivergenceStopCriterium(0.5, 15);
-            Assert.Throws<ArgumentNullException>(() => criterium.DetermineStatus(
-                1,
-                DenseVector.Create(3, i => 4),
-                DenseVector.Create(3, i => 5),
-                null));
-        }
-
         /// <summary>
         /// Can determine status with too few iterations.
         /// </summary>
@@ -152,7 +138,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex32.Solvers.StopCr
                     new DenseVector(new[] {new Complex32(1.0f, 0)}),
                     new DenseVector(new[] {new Complex32(1.0f, 0)}),
                     new DenseVector(new[] {new Complex32((i + 1)*(Increase + 0.1f), 0)}));
-                Assert.IsInstanceOf(typeof (CalculationRunning), status, "Status check fail.");
+                Assert.AreEqual(IterationStatus.Running, status, "Status check fail.");
             }
         }
 
@@ -176,7 +162,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex32.Solvers.StopCr
                     new DenseVector(new[] {new Complex32(1.0f, 0)}),
                     new DenseVector(new[] {new Complex32((i + 1)*(Increase - 0.01f), 0)}));
 
-                Assert.IsInstanceOf(typeof (CalculationRunning), status, "Status check fail.");
+                Assert.AreEqual(IterationStatus.Running, status, "Status check fail.");
             }
         }
 
@@ -200,7 +186,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex32.Solvers.StopCr
                     new DenseVector(new[] {new Complex32(1.0f, 0)}),
                     new DenseVector(new[] {new Complex32((i + 1)*(Increase - 0.01f), 0)}));
 
-                Assert.IsInstanceOf(typeof (CalculationRunning), status, "Status check fail.");
+                Assert.AreEqual(IterationStatus.Running, status, "Status check fail.");
             }
 
             // Now make it fail by throwing in a NaN
@@ -210,7 +196,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex32.Solvers.StopCr
                 new DenseVector(new[] {new Complex32(1.0f, 0)}),
                 new DenseVector(new[] {new Complex32(float.NaN, 0)}));
 
-            Assert.IsInstanceOf(typeof (CalculationDiverged), status2, "Status check fail.");
+            Assert.AreEqual(IterationStatus.Diverged, status2, "Status check fail.");
         }
 
         /// <summary>
@@ -235,7 +221,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex32.Solvers.StopCr
                     new DenseVector(new[] {new Complex32(1.0f, 0)}),
                     new DenseVector(new[] {new Complex32(previous, 0)}));
 
-                Assert.IsInstanceOf(typeof (CalculationRunning), status, "Status check fail.");
+                Assert.AreEqual(IterationStatus.Running, status, "Status check fail.");
             }
 
             // Add the final residual. Now we should have divergence
@@ -246,7 +232,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex32.Solvers.StopCr
                 new DenseVector(new[] {new Complex32(1.0f, 0)}),
                 new DenseVector(new[] {new Complex32(previous, 0)}));
 
-            Assert.IsInstanceOf(typeof (CalculationDiverged), status2, "Status check fail.");
+            Assert.AreEqual(IterationStatus.Diverged, status2, "Status check fail.");
         }
 
         /// <summary>
@@ -267,14 +253,14 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex32.Solvers.StopCr
                 new DenseVector(new[] {new Complex32(1.0f, 0)}),
                 new DenseVector(new[] {new Complex32(float.NaN, 0)}));
 
-            Assert.IsInstanceOf(typeof (CalculationDiverged), status, "Status check fail.");
+            Assert.AreEqual(IterationStatus.Diverged, status, "Status check fail.");
 
             // Reset the state
             criterium.ResetToPrecalculationState();
 
             Assert.AreEqual(Increase, criterium.MaximumRelativeIncrease, "Incorrect maximum");
             Assert.AreEqual(Iterations, criterium.MinimumNumberOfIterations, "Incorrect iteration count");
-            Assert.IsInstanceOf(typeof (CalculationIndetermined), criterium.Status, "Status check fail.");
+            Assert.AreEqual(IterationStatus.Indetermined, criterium.Status, "Status check fail.");
         }
 
         /// <summary>
diff --git a/src/UnitTests/LinearAlgebraTests/Complex32/Solvers/StopCriterium/FailureStopCriteriumTest.cs b/src/UnitTests/LinearAlgebraTests/Complex32/Solvers/StopCriterium/FailureStopCriteriumTest.cs
index 98bf9722..ce1fc772 100644
--- a/src/UnitTests/LinearAlgebraTests/Complex32/Solvers/StopCriterium/FailureStopCriteriumTest.cs
+++ b/src/UnitTests/LinearAlgebraTests/Complex32/Solvers/StopCriterium/FailureStopCriteriumTest.cs
@@ -28,11 +28,11 @@
 // OTHER DEALINGS IN THE SOFTWARE.
 // </copyright>
 
+using System;
 using MathNet.Numerics.LinearAlgebra.Complex32;
 using MathNet.Numerics.LinearAlgebra.Complex32.Solvers.StopCriterium;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
+using MathNet.Numerics.LinearAlgebra.Solvers;
 using NUnit.Framework;
-using System;
 
 namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex32.Solvers.StopCriterium
 {
@@ -66,30 +66,6 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex32.Solvers.StopCr
             Assert.Throws<ArgumentOutOfRangeException>(() => criterium.DetermineStatus(-1, DenseVector.Create(3, i => 4), DenseVector.Create(3, i => 5), DenseVector.Create(3, i => 6)));
         }
 
-        /// <summary>
-        /// Determine status with <c>null</c> solution vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullSolutionVectorThrowsArgumentNullException()
-        {
-            var criterium = new FailureStopCriterium();
-            Assert.IsNotNull(criterium, "There should be a criterium");
-
-            Assert.Throws<ArgumentNullException>(() => criterium.DetermineStatus(1, null, DenseVector.Create(3, i => 6), DenseVector.Create(4, i => 4)));
-        }
-
-        /// <summary>
-        /// Determine status with <c>null</c> residual vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullResidualVectorThrowsArgumentNullException()
-        {
-            var criterium = new FailureStopCriterium();
-            Assert.IsNotNull(criterium, "There should be a criterium");
-
-            Assert.Throws<ArgumentNullException>(() => criterium.DetermineStatus(1, DenseVector.Create(3, i => 4), DenseVector.Create(3, i => 6), null));
-        }
-
         /// <summary>
         /// Determine status with non-matching vectors throws <c>ArgumentException</c>.
         /// </summary>
@@ -116,7 +92,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex32.Solvers.StopCr
             var residual = new DenseVector(new[] {new Complex32(1000, 0), new Complex32(float.NaN, 0), new Complex32(2001, 0)});
 
             var status = criterium.DetermineStatus(5, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationFailure), status, "Should be failed");
+            Assert.AreEqual(IterationStatus.Failure, status, "Should be failed");
         }
 
         /// <summary>
@@ -133,7 +109,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex32.Solvers.StopCr
             var residual = new DenseVector(new[] {new Complex32(1000, 0), new Complex32(1000, 0), new Complex32(2001, 0)});
 
             var status = criterium.DetermineStatus(5, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationFailure), status, "Should be failed");
+            Assert.AreEqual(IterationStatus.Failure, status, "Should be failed");
         }
 
         /// <summary>
@@ -150,7 +126,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex32.Solvers.StopCr
             var residual = new DenseVector(new[] {new Complex32(1.0f, 0), new Complex32(2.0f, 0), new Complex32(3, 0)});
 
             var status = criterium.DetermineStatus(5, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationRunning), status, "Should be running");
+            Assert.AreEqual(IterationStatus.Running, status, "Should be running");
         }
 
         /// <summary>
@@ -167,10 +143,10 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex32.Solvers.StopCr
             var residual = new DenseVector(new[] {new Complex32(1000, 0), new Complex32(1000, 0), new Complex32(2001, 0)});
 
             var status = criterium.DetermineStatus(5, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationRunning), status, "Should be running");
+            Assert.AreEqual(IterationStatus.Running, status, "Should be running");
 
             criterium.ResetToPrecalculationState();
-            Assert.IsInstanceOf(typeof (CalculationIndetermined), criterium.Status, "Should not have started");
+            Assert.AreEqual(IterationStatus.Indetermined, criterium.Status, "Should not have started");
         }
 
         /// <summary>
diff --git a/src/UnitTests/LinearAlgebraTests/Complex32/Solvers/StopCriterium/IterationCountStopCriteriumTest.cs b/src/UnitTests/LinearAlgebraTests/Complex32/Solvers/StopCriterium/IterationCountStopCriteriumTest.cs
index a6cfa27e..8fa01ba5 100644
--- a/src/UnitTests/LinearAlgebraTests/Complex32/Solvers/StopCriterium/IterationCountStopCriteriumTest.cs
+++ b/src/UnitTests/LinearAlgebraTests/Complex32/Solvers/StopCriterium/IterationCountStopCriteriumTest.cs
@@ -31,7 +31,6 @@
 using System;
 using MathNet.Numerics.LinearAlgebra.Complex32;
 using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using NUnit.Framework;
 
 namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex32.Solvers.StopCriterium
@@ -100,10 +99,10 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex32.Solvers.StopCr
             Assert.IsNotNull(criterium, "A criterium should have been created");
 
             var status = criterium.DetermineStatus(5, DenseVector.Create(3, i => 1), DenseVector.Create(3, i => 2), DenseVector.Create(3, i => 3));
-            Assert.IsInstanceOf(typeof (CalculationRunning), status, "Should be running");
+            Assert.AreEqual(IterationStatus.Running, status, "Should be running");
 
             var status2 = criterium.DetermineStatus(10, DenseVector.Create(3, i => 1), DenseVector.Create(3, i => 2), DenseVector.Create(3, i => 3));
-            Assert.IsInstanceOf(typeof (CalculationStoppedWithoutConvergence), status2, "Should be finished");
+            Assert.AreEqual(IterationStatus.StoppedWithoutConvergence, status2, "Should be finished");
         }
 
         /// <summary>
@@ -116,10 +115,10 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex32.Solvers.StopCr
             Assert.IsNotNull(criterium, "A criterium should have been created");
 
             var status = criterium.DetermineStatus(5, DenseVector.Create(3, i => 1), DenseVector.Create(3, i => 2), DenseVector.Create(3, i => 3));
-            Assert.IsInstanceOf(typeof (CalculationRunning), status, "Should be running");
+            Assert.AreEqual(IterationStatus.Running, status, "Should be running");
 
             criterium.ResetToPrecalculationState();
-            Assert.IsInstanceOf(typeof (CalculationIndetermined), criterium.Status, "Should not have started");
+            Assert.AreEqual(IterationStatus.Indetermined, criterium.Status, "Should not have started");
         }
 
         /// <summary>
diff --git a/src/UnitTests/LinearAlgebraTests/Complex32/Solvers/StopCriterium/ResidualStopCriteriumTest.cs b/src/UnitTests/LinearAlgebraTests/Complex32/Solvers/StopCriterium/ResidualStopCriteriumTest.cs
index 19f6cce4..34170a44 100644
--- a/src/UnitTests/LinearAlgebraTests/Complex32/Solvers/StopCriterium/ResidualStopCriteriumTest.cs
+++ b/src/UnitTests/LinearAlgebraTests/Complex32/Solvers/StopCriterium/ResidualStopCriteriumTest.cs
@@ -28,11 +28,11 @@
 // OTHER DEALINGS IN THE SOFTWARE.
 // </copyright>
 
+using System;
 using MathNet.Numerics.LinearAlgebra.Complex32;
 using MathNet.Numerics.LinearAlgebra.Complex32.Solvers.StopCriterium;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
+using MathNet.Numerics.LinearAlgebra.Solvers;
 using NUnit.Framework;
-using System;
 
 namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex32.Solvers.StopCriterium
 {
@@ -117,54 +117,6 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex32.Solvers.StopCr
                 DenseVector.Create(3, i => 6)));
         }
 
-        /// <summary>
-        /// Determine status with <c>null</c> solution vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullSolutionVectorThrowsArgumentNullException()
-        {
-            var criterium = new ResidualStopCriterium(1e-6f, 50);
-            Assert.IsNotNull(criterium, "There should be a criterium");
-
-            Assert.Throws<ArgumentNullException>(() => criterium.DetermineStatus(
-                1,
-                null,
-                DenseVector.Create(3, i => 5),
-                DenseVector.Create(3, i => 6)));
-        }
-
-        /// <summary>
-        /// Determine status with <c>null</c> source vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullSourceVectorThrowsArgumentNullException()
-        {
-            var criterium = new ResidualStopCriterium(1e-6f, 50);
-            Assert.IsNotNull(criterium, "There should be a criterium");
-
-            Assert.Throws<ArgumentNullException>(() => criterium.DetermineStatus(
-                1,
-                DenseVector.Create(3, i => 4),
-                null,
-                DenseVector.Create(3, i => 6)));
-        }
-
-        /// <summary>
-        /// Determine status with <c>null</c> residual vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullResidualVectorThrowsArgumentNullException()
-        {
-            var criterium = new ResidualStopCriterium(1e-6f, 50);
-            Assert.IsNotNull(criterium, "There should be a criterium");
-
-            Assert.Throws<ArgumentNullException>(() => criterium.DetermineStatus(
-                1,
-                DenseVector.Create(3, i => 4),
-                DenseVector.Create(3, i => 5),
-                null));
-        }
-
         /// <summary>
         /// Determine status with non-matching solution vector throws <c>ArgumentException</c>.
         /// </summary>
@@ -227,7 +179,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex32.Solvers.StopCr
             var residual = new DenseVector(new[] {new Complex32(1000.0f, 1), new Complex32(1000.0f, 1), new Complex32(2001.0f, 1)});
 
             var status = criterium.DetermineStatus(5, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationDiverged), status, "Should be diverged");
+            Assert.AreEqual(IterationStatus.Diverged, status, "Should be diverged");
         }
 
         /// <summary>
@@ -244,7 +196,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex32.Solvers.StopCr
             var residual = new DenseVector(new[] {new Complex32(1000.0f, 1), new Complex32(float.NaN, 1), new Complex32(2001.0f, 1)});
 
             var status = criterium.DetermineStatus(5, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationDiverged), status, "Should be diverged");
+            Assert.AreEqual(IterationStatus.Diverged, status, "Should be diverged");
         }
 
         /// <summary>
@@ -265,7 +217,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex32.Solvers.StopCr
             var residual = new DenseVector(new[] {Complex32.Zero, Complex32.Zero, Complex32.Zero});
 
             var status = criterium.DetermineStatus(0, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationConverged), status, "Should be done");
+            Assert.AreEqual(IterationStatus.Converged, status, "Should be done");
         }
 
         /// <summary>
@@ -287,10 +239,10 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex32.Solvers.StopCr
             var residual = new DenseVector(new[] {new Complex32(0.001f, 0), new Complex32(0.001f, 0), new Complex32(0.002f, 0)});
 
             var status = criterium.DetermineStatus(5, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationRunning), status, "Should still be running");
+            Assert.AreEqual(IterationStatus.Running, status, "Should still be running");
 
             var status2 = criterium.DetermineStatus(16, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationConverged), status2, "Should be done");
+            Assert.AreEqual(IterationStatus.Converged, status2, "Should be done");
         }
 
         /// <summary>
@@ -307,10 +259,10 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Complex32.Solvers.StopCr
             var residual = new DenseVector(new[] {new Complex32(1.000f, 0), new Complex32(1.000f, 0), new Complex32(2.001f, 0)});
 
             var status = criterium.DetermineStatus(5, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationRunning), status, "Should be running");
+            Assert.AreEqual(IterationStatus.Running, status, "Should be running");
 
             criterium.ResetToPrecalculationState();
-            Assert.IsInstanceOf(typeof (CalculationIndetermined), criterium.Status, "Should not have started");
+            Assert.AreEqual(IterationStatus.Indetermined, criterium.Status, "Should not have started");
         }
 
         /// <summary>
diff --git a/src/UnitTests/LinearAlgebraTests/Double/Solvers/IteratorTest.cs b/src/UnitTests/LinearAlgebraTests/Double/Solvers/IteratorTest.cs
index 8b8fbc8e..67e79eb1 100644
--- a/src/UnitTests/LinearAlgebraTests/Double/Solvers/IteratorTest.cs
+++ b/src/UnitTests/LinearAlgebraTests/Double/Solvers/IteratorTest.cs
@@ -33,7 +33,6 @@ using System.Collections.Generic;
 using MathNet.Numerics.LinearAlgebra.Double;
 using MathNet.Numerics.LinearAlgebra.Double.Solvers.StopCriterium;
 using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using NUnit.Framework;
 
 namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double.Solvers
@@ -80,72 +79,6 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double.Solvers
                 DenseVector.Create(3, i => 6)));
         }
 
-        /// <summary>
-        /// Determine status with <c>null</c> solution vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullSolutionVectorThrowsArgumentNullException()
-        {
-            var criteria = new List<IIterationStopCriterium<double>>
-                {
-                    new FailureStopCriterium(),
-                    new DivergenceStopCriterium(),
-                    new IterationCountStopCriterium<double>(),
-                    new ResidualStopCriterium()
-                };
-            var iterator = new Iterator<double>(criteria);
-
-            Assert.Throws<ArgumentNullException>(() => iterator.DetermineStatus(
-                1,
-                null,
-                DenseVector.Create(3, i => 5),
-                DenseVector.Create(3, i => 6)));
-        }
-
-        /// <summary>
-        /// Determine status with <c>null</c> source vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullSourceVectorThrowsArgumentNullException()
-        {
-            var criteria = new List<IIterationStopCriterium<double>>
-                {
-                    new FailureStopCriterium(),
-                    new DivergenceStopCriterium(),
-                    new IterationCountStopCriterium<double>(),
-                    new ResidualStopCriterium()
-                };
-            var iterator = new Iterator<double>(criteria);
-
-            Assert.Throws<ArgumentNullException>(() => iterator.DetermineStatus(
-                1,
-                DenseVector.Create(3, i => 5),
-                null,
-                DenseVector.Create(3, i => 6)));
-        }
-
-        /// <summary>
-        /// Determine status with <c>null</c> residual vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullResidualVectorThrowsArgumentNullException()
-        {
-            var criteria = new List<IIterationStopCriterium<double>>
-                {
-                    new FailureStopCriterium(),
-                    new DivergenceStopCriterium(),
-                    new IterationCountStopCriterium<double>(),
-                    new ResidualStopCriterium()
-                };
-            var iterator = new Iterator<double>(criteria);
-
-            Assert.Throws<ArgumentNullException>(() => iterator.DetermineStatus(
-                1,
-                DenseVector.Create(3, i => 4),
-                DenseVector.Create(3, i => 5),
-                null));
-        }
-
         /// <summary>
         /// Can determine status.
         /// </summary>
@@ -167,7 +100,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double.Solvers
                 DenseVector.Create(3, i => 4),
                 DenseVector.Create(3, i => 4),
                 DenseVector.Create(3, i => 4));
-            Assert.IsInstanceOf(typeof (CalculationRunning), iterator.Status, "Incorrect status");
+            Assert.AreEqual(IterationStatus.Running, iterator.Status, "Incorrect status");
 
             // Second step, should run out of iterations.
             iterator.DetermineStatus(
@@ -175,7 +108,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double.Solvers
                 DenseVector.Create(3, i => 4),
                 DenseVector.Create(3, i => 4),
                 DenseVector.Create(3, i => 4));
-            Assert.IsInstanceOf(typeof (CalculationStoppedWithoutConvergence), iterator.Status, "Incorrect status");
+            Assert.AreEqual(IterationStatus.StoppedWithoutConvergence, iterator.Status, "Incorrect status");
         }
 
         /// <summary>
@@ -199,13 +132,13 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double.Solvers
                 DenseVector.Create(3, i => 4),
                 DenseVector.Create(3, i => 4),
                 DenseVector.Create(3, i => 4));
-            Assert.IsInstanceOf(typeof (CalculationRunning), iterator.Status, "Incorrect status");
+            Assert.AreEqual(IterationStatus.Running, iterator.Status, "Incorrect status");
 
             iterator.Reset();
-            Assert.IsInstanceOf(typeof (CalculationIndetermined), iterator.Status, "Incorrect status");
-            Assert.IsInstanceOf(typeof (CalculationIndetermined), criteria[0].Status, "Incorrect status");
-            Assert.IsInstanceOf(typeof (CalculationIndetermined), criteria[1].Status, "Incorrect status");
-            Assert.IsInstanceOf(typeof (CalculationIndetermined), criteria[2].Status, "Incorrect status");
+            Assert.AreEqual(IterationStatus.Indetermined, iterator.Status, "Incorrect status");
+            Assert.AreEqual(IterationStatus.Indetermined, criteria[0].Status, "Incorrect status");
+            Assert.AreEqual(IterationStatus.Indetermined, criteria[1].Status, "Incorrect status");
+            Assert.AreEqual(IterationStatus.Indetermined, criteria[2].Status, "Incorrect status");
         }
     }
 }
diff --git a/src/UnitTests/LinearAlgebraTests/Double/Solvers/StopCriterium/DivergenceStopCriteriumTest.cs b/src/UnitTests/LinearAlgebraTests/Double/Solvers/StopCriterium/DivergenceStopCriteriumTest.cs
index f29581ca..b2b94922 100644
--- a/src/UnitTests/LinearAlgebraTests/Double/Solvers/StopCriterium/DivergenceStopCriteriumTest.cs
+++ b/src/UnitTests/LinearAlgebraTests/Double/Solvers/StopCriterium/DivergenceStopCriteriumTest.cs
@@ -28,11 +28,11 @@
 // OTHER DEALINGS IN THE SOFTWARE.
 // </copyright>
 
+using System;
 using MathNet.Numerics.LinearAlgebra.Double;
 using MathNet.Numerics.LinearAlgebra.Double.Solvers.StopCriterium;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
+using MathNet.Numerics.LinearAlgebra.Solvers;
 using NUnit.Framework;
-using System;
 
 namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double.Solvers.StopCriterium
 {
@@ -117,20 +117,6 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double.Solvers.StopCrite
                 DenseVector.Create(3, i => 6)));
         }
 
-        /// <summary>
-        /// Determine status with <c>null</c> residual vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullResidualVectorThrowsArgumentNullException()
-        {
-            var criterium = new DivergenceStopCriterium(0.5, 15);
-            Assert.Throws<ArgumentNullException>(() => criterium.DetermineStatus(
-                1,
-                DenseVector.Create(3, i => 4),
-                DenseVector.Create(3, i => 5),
-                null));
-        }
-
         /// <summary>
         /// Can determine status with too few iterations.
         /// </summary>
@@ -151,7 +137,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double.Solvers.StopCrite
                     new DenseVector(new[] {1.0}),
                     new DenseVector(new[] {(i + 1)*(Increase + 0.1)}));
 
-                Assert.IsInstanceOf(typeof (CalculationRunning), status, "Status check fail.");
+                Assert.AreEqual(IterationStatus.Running, status, "Status check fail.");
             }
         }
 
@@ -175,7 +161,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double.Solvers.StopCrite
                     new DenseVector(new[] {1.0}),
                     new DenseVector(new[] {(i + 1)*(Increase - 0.01)}));
 
-                Assert.IsInstanceOf(typeof (CalculationRunning), status, "Status check fail.");
+                Assert.AreEqual(IterationStatus.Running, status, "Status check fail.");
             }
         }
 
@@ -199,7 +185,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double.Solvers.StopCrite
                     new DenseVector(new[] {1.0}),
                     new DenseVector(new[] {(i + 1)*(Increase - 0.01)}));
 
-                Assert.IsInstanceOf(typeof (CalculationRunning), status, "Status check fail.");
+                Assert.AreEqual(IterationStatus.Running, status, "Status check fail.");
             }
 
             // Now make it fail by throwing in a NaN
@@ -209,7 +195,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double.Solvers.StopCrite
                 new DenseVector(new[] {1.0}),
                 new DenseVector(new[] {double.NaN}));
 
-            Assert.IsInstanceOf(typeof (CalculationDiverged), status2, "Status check fail.");
+            Assert.AreEqual(IterationStatus.Diverged, status2, "Status check fail.");
         }
 
         /// <summary>
@@ -234,7 +220,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double.Solvers.StopCrite
                     new DenseVector(new[] {1.0}),
                     new DenseVector(new[] {previous}));
 
-                Assert.IsInstanceOf(typeof (CalculationRunning), status, "Status check fail.");
+                Assert.AreEqual(IterationStatus.Running, status, "Status check fail.");
             }
 
             // Add the final residual. Now we should have divergence
@@ -245,7 +231,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double.Solvers.StopCrite
                 new DenseVector(new[] {1.0}),
                 new DenseVector(new[] {previous}));
 
-            Assert.IsInstanceOf(typeof (CalculationDiverged), status2, "Status check fail.");
+            Assert.AreEqual(IterationStatus.Diverged, status2, "Status check fail.");
         }
 
         /// <summary>
@@ -266,14 +252,14 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double.Solvers.StopCrite
                 new DenseVector(new[] {1.0}),
                 new DenseVector(new[] {double.NaN}));
 
-            Assert.IsInstanceOf(typeof (CalculationDiverged), status, "Status check fail.");
+            Assert.AreEqual(IterationStatus.Diverged, status, "Status check fail.");
 
             // Reset the state
             criterium.ResetToPrecalculationState();
 
             Assert.AreEqual(Increase, criterium.MaximumRelativeIncrease, "Incorrect maximum");
             Assert.AreEqual(Iterations, criterium.MinimumNumberOfIterations, "Incorrect iteration count");
-            Assert.IsInstanceOf(typeof (CalculationIndetermined), criterium.Status, "Status check fail.");
+            Assert.AreEqual(IterationStatus.Indetermined, criterium.Status, "Status check fail.");
         }
 
         /// <summary>
diff --git a/src/UnitTests/LinearAlgebraTests/Double/Solvers/StopCriterium/FailureStopCriteriumTest.cs b/src/UnitTests/LinearAlgebraTests/Double/Solvers/StopCriterium/FailureStopCriteriumTest.cs
index dbd14365..97a9710c 100644
--- a/src/UnitTests/LinearAlgebraTests/Double/Solvers/StopCriterium/FailureStopCriteriumTest.cs
+++ b/src/UnitTests/LinearAlgebraTests/Double/Solvers/StopCriterium/FailureStopCriteriumTest.cs
@@ -30,7 +30,7 @@
 
 using MathNet.Numerics.LinearAlgebra.Double;
 using MathNet.Numerics.LinearAlgebra.Double.Solvers.StopCriterium;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
+using MathNet.Numerics.LinearAlgebra.Solvers;
 using NUnit.Framework;
 using System;
 
@@ -64,30 +64,6 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double.Solvers.StopCrite
             Assert.Throws<ArgumentOutOfRangeException>(() => criterium.DetermineStatus(-1, DenseVector.Create(3, i => 4), DenseVector.Create(3, i => 5), DenseVector.Create(3, i => 6)));
         }
 
-        /// <summary>
-        /// Determine status with <c>null</c> solution vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullSolutionVectorThrowsArgumentNullException()
-        {
-            var criterium = new FailureStopCriterium();
-            Assert.IsNotNull(criterium, "There should be a criterium");
-
-            Assert.Throws<ArgumentNullException>(() => criterium.DetermineStatus(1, null, DenseVector.Create(3, i => 6), DenseVector.Create(4, i => 4)));
-        }
-
-        /// <summary>
-        /// Determine status with <c>null</c> residual vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullResidualVectorThrowsArgumentNullException()
-        {
-            var criterium = new FailureStopCriterium();
-            Assert.IsNotNull(criterium, "There should be a criterium");
-
-            Assert.Throws<ArgumentNullException>(() => criterium.DetermineStatus(1, DenseVector.Create(3, i => 4), DenseVector.Create(3, i => 6), null));
-        }
-
         /// <summary>
         /// Determine status with non-matching vectors throws <c>ArgumentException</c>.
         /// </summary>
@@ -114,7 +90,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double.Solvers.StopCrite
             var residual = new DenseVector(new[] { 1000, double.NaN, 2001 });
 
             var status = criterium.DetermineStatus(5, solution, source, residual);
-            Assert.IsInstanceOf(typeof(CalculationFailure), status, "Should be failed");
+            Assert.AreEqual(IterationStatus.Failure, status, "Should be failed");
         }
 
         /// <summary>
@@ -131,7 +107,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double.Solvers.StopCrite
             var residual = new DenseVector(new[] { 1000.0, 1000.0, 2001.0 });
 
             var status = criterium.DetermineStatus(5, solution, source, residual);
-            Assert.IsInstanceOf(typeof(CalculationFailure), status, "Should be failed");
+            Assert.AreEqual(IterationStatus.Failure, status, "Should be failed");
         }
 
         /// <summary>
@@ -148,7 +124,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double.Solvers.StopCrite
             var residual = new DenseVector(new[] { 1.0, 2.0, 3.0 });
 
             var status = criterium.DetermineStatus(5, solution, source, residual);
-            Assert.IsInstanceOf(typeof(CalculationRunning), status, "Should be running");
+            Assert.AreEqual(IterationStatus.Running, status, "Should be running");
         }
 
         /// <summary>
@@ -165,10 +141,10 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double.Solvers.StopCrite
             var residual = new DenseVector(new[] { 1000.0, 1000.0, 2001.0 });
 
             var status = criterium.DetermineStatus(5, solution, source, residual);
-            Assert.IsInstanceOf(typeof(CalculationRunning), status, "Should be running");
+            Assert.AreEqual(IterationStatus.Running, status, "Should be running");
 
             criterium.ResetToPrecalculationState();
-            Assert.IsInstanceOf(typeof(CalculationIndetermined), criterium.Status, "Should not have started");
+            Assert.AreEqual(IterationStatus.Indetermined, criterium.Status, "Should not have started");
         }
 
         /// <summary>
diff --git a/src/UnitTests/LinearAlgebraTests/Double/Solvers/StopCriterium/IterationCountStopCriteriumTest.cs b/src/UnitTests/LinearAlgebraTests/Double/Solvers/StopCriterium/IterationCountStopCriteriumTest.cs
index 22b579aa..f133235e 100644
--- a/src/UnitTests/LinearAlgebraTests/Double/Solvers/StopCriterium/IterationCountStopCriteriumTest.cs
+++ b/src/UnitTests/LinearAlgebraTests/Double/Solvers/StopCriterium/IterationCountStopCriteriumTest.cs
@@ -31,7 +31,6 @@
 using System;
 using MathNet.Numerics.LinearAlgebra.Double;
 using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using NUnit.Framework;
 
 namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double.Solvers.StopCriterium
@@ -98,10 +97,10 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double.Solvers.StopCrite
             Assert.IsNotNull(criterium, "A criterium should have been created");
 
             var status = criterium.DetermineStatus(5, DenseVector.Create(3, i => 1), DenseVector.Create(3, i => 2), DenseVector.Create(3, i => 3));
-            Assert.IsInstanceOf(typeof (CalculationRunning), status, "Should be running");
+            Assert.AreEqual(IterationStatus.Running, status, "Should be running");
 
             var status2 = criterium.DetermineStatus(10, DenseVector.Create(3, i => 1), DenseVector.Create(3, i => 2), DenseVector.Create(3, i => 3));
-            Assert.IsInstanceOf(typeof (CalculationStoppedWithoutConvergence), status2, "Should be finished");
+            Assert.AreEqual(IterationStatus.StoppedWithoutConvergence, status2, "Should be finished");
         }
 
         /// <summary>
@@ -114,10 +113,10 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double.Solvers.StopCrite
             Assert.IsNotNull(criterium, "A criterium should have been created");
 
             var status = criterium.DetermineStatus(5, DenseVector.Create(3, i => 1), DenseVector.Create(3, i => 2), DenseVector.Create(3, i => 3));
-            Assert.IsInstanceOf(typeof (CalculationRunning), status, "Should be running");
+            Assert.AreEqual(IterationStatus.Running, status, "Should be running");
 
             criterium.ResetToPrecalculationState();
-            Assert.IsInstanceOf(typeof (CalculationIndetermined), criterium.Status, "Should not have started");
+            Assert.AreEqual(IterationStatus.Indetermined, criterium.Status, "Should not have started");
         }
 
         /// <summary>
diff --git a/src/UnitTests/LinearAlgebraTests/Double/Solvers/StopCriterium/ResidualStopCriteriumTest.cs b/src/UnitTests/LinearAlgebraTests/Double/Solvers/StopCriterium/ResidualStopCriteriumTest.cs
index e9faa742..5ae0bc1b 100644
--- a/src/UnitTests/LinearAlgebraTests/Double/Solvers/StopCriterium/ResidualStopCriteriumTest.cs
+++ b/src/UnitTests/LinearAlgebraTests/Double/Solvers/StopCriterium/ResidualStopCriteriumTest.cs
@@ -28,11 +28,11 @@
 // OTHER DEALINGS IN THE SOFTWARE.
 // </copyright>
 
+using System;
 using MathNet.Numerics.LinearAlgebra.Double;
 using MathNet.Numerics.LinearAlgebra.Double.Solvers.StopCriterium;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
+using MathNet.Numerics.LinearAlgebra.Solvers;
 using NUnit.Framework;
-using System;
 
 namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double.Solvers.StopCriterium
 {
@@ -115,54 +115,6 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double.Solvers.StopCrite
                 DenseVector.Create(3, i => 6)));
         }
 
-        /// <summary>
-        /// Determine status with <c>null</c> solution vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullSolutionVectorThrowsArgumentNullException()
-        {
-            var criterium = new ResidualStopCriterium(1e-8, 50);
-            Assert.IsNotNull(criterium, "There should be a criterium");
-
-            Assert.Throws<ArgumentNullException>(() => criterium.DetermineStatus(
-                1,
-                null,
-                DenseVector.Create(3, i => 5),
-                DenseVector.Create(3, i => 6)));
-        }
-
-        /// <summary>
-        /// Determine status with <c>null</c> source vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullSourceVectorThrowsArgumentNullException()
-        {
-            var criterium = new ResidualStopCriterium(1e-8, 50);
-            Assert.IsNotNull(criterium, "There should be a criterium");
-
-            Assert.Throws<ArgumentNullException>(() => criterium.DetermineStatus(
-                1,
-                DenseVector.Create(3, i => 4),
-                null,
-                DenseVector.Create(3, i => 6)));
-        }
-
-        /// <summary>
-        /// Determine status with <c>null</c> residual vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullResidualVectorThrowsArgumentNullException()
-        {
-            var criterium = new ResidualStopCriterium(1e-8, 50);
-            Assert.IsNotNull(criterium, "There should be a criterium");
-
-            Assert.Throws<ArgumentNullException>(() => criterium.DetermineStatus(
-                1,
-                DenseVector.Create(3, i => 4),
-                DenseVector.Create(3, i => 5),
-                null));
-        }
-
         /// <summary>
         /// Determine status with non-matching solution vector throws <c>ArgumentException</c>.
         /// </summary>
@@ -225,7 +177,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double.Solvers.StopCrite
             var residual = new DenseVector(new[] {1000.0, 1000.0, 2001.0});
 
             var status = criterium.DetermineStatus(5, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationDiverged), status, "Should be diverged");
+            Assert.AreEqual(IterationStatus.Diverged, status, "Should be diverged");
         }
 
         /// <summary>
@@ -242,7 +194,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double.Solvers.StopCrite
             var residual = new DenseVector(new[] {1000.0, double.NaN, 2001.0});
 
             var status = criterium.DetermineStatus(5, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationDiverged), status, "Should be diverged");
+            Assert.AreEqual(IterationStatus.Diverged, status, "Should be diverged");
         }
 
         /// <summary>
@@ -259,7 +211,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double.Solvers.StopCrite
             var residual = new DenseVector(new[] {0.0, 0.0, 0.0});
 
             var status = criterium.DetermineStatus(0, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationConverged), status, "Should be done");
+            Assert.AreEqual(IterationStatus.Converged, status, "Should be done");
         }
 
         /// <summary>
@@ -281,10 +233,10 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double.Solvers.StopCrite
             var residual = new DenseVector(new[] {0.001, 0.001, 0.002});
 
             var status = criterium.DetermineStatus(5, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationRunning), status, "Should still be running");
+            Assert.AreEqual(IterationStatus.Running, status, "Should still be running");
 
             var status2 = criterium.DetermineStatus(16, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationConverged), status2, "Should be done");
+            Assert.AreEqual(IterationStatus.Converged, status2, "Should be done");
         }
 
         /// <summary>
@@ -301,10 +253,10 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double.Solvers.StopCrite
             var residual = new DenseVector(new[] {1.000, 1.000, 2.001});
 
             var status = criterium.DetermineStatus(5, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationRunning), status, "Should be running");
+            Assert.AreEqual(IterationStatus.Running, status, "Should be running");
 
             criterium.ResetToPrecalculationState();
-            Assert.IsInstanceOf(typeof (CalculationIndetermined), criterium.Status, "Should not have started");
+            Assert.AreEqual(IterationStatus.Indetermined, criterium.Status, "Should not have started");
         }
 
         /// <summary>
diff --git a/src/UnitTests/LinearAlgebraTests/Single/Solvers/IteratorTest.cs b/src/UnitTests/LinearAlgebraTests/Single/Solvers/IteratorTest.cs
index 81948de5..41fd2e70 100644
--- a/src/UnitTests/LinearAlgebraTests/Single/Solvers/IteratorTest.cs
+++ b/src/UnitTests/LinearAlgebraTests/Single/Solvers/IteratorTest.cs
@@ -33,7 +33,6 @@ using System.Collections.Generic;
 using MathNet.Numerics.LinearAlgebra.Single;
 using MathNet.Numerics.LinearAlgebra.Single.Solvers.StopCriterium;
 using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using NUnit.Framework;
 
 namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Single.Solvers
@@ -80,72 +79,6 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Single.Solvers
                 DenseVector.Create(3, i => 6)));
         }
 
-        /// <summary>
-        /// Determine status with <c>null</c> solution vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullSolutionVectorThrowsArgumentNullException()
-        {
-            var criteria = new List<IIterationStopCriterium<float>>
-                {
-                    new FailureStopCriterium(),
-                    new DivergenceStopCriterium(),
-                    new IterationCountStopCriterium<float>(),
-                    new ResidualStopCriterium()
-                };
-            var iterator = new Iterator<float>(criteria);
-
-            Assert.Throws<ArgumentNullException>(() => iterator.DetermineStatus(
-                1,
-                null,
-                DenseVector.Create(3, i => 5),
-                DenseVector.Create(3, i => 6)));
-        }
-
-        /// <summary>
-        /// Determine status with <c>null</c> source vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullSourceVectorThrowsArgumentNullException()
-        {
-            var criteria = new List<IIterationStopCriterium<float>>
-                {
-                    new FailureStopCriterium(),
-                    new DivergenceStopCriterium(),
-                    new IterationCountStopCriterium<float>(),
-                    new ResidualStopCriterium()
-                };
-            var iterator = new Iterator<float>(criteria);
-
-            Assert.Throws<ArgumentNullException>(() => iterator.DetermineStatus(
-                1,
-                DenseVector.Create(3, i => 5),
-                null,
-                DenseVector.Create(3, i => 6)));
-        }
-
-        /// <summary>
-        /// Determine status with <c>null</c> residual vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullResidualVectorThrowsArgumentNullException()
-        {
-            var criteria = new List<IIterationStopCriterium<float>>
-                {
-                    new FailureStopCriterium(),
-                    new DivergenceStopCriterium(),
-                    new IterationCountStopCriterium<float>(),
-                    new ResidualStopCriterium()
-                };
-            var iterator = new Iterator<float>(criteria);
-
-            Assert.Throws<ArgumentNullException>(() => iterator.DetermineStatus(
-                1,
-                DenseVector.Create(3, i => 4),
-                DenseVector.Create(3, i => 5),
-                null));
-        }
-
         /// <summary>
         /// Can determine status.
         /// </summary>
@@ -167,7 +100,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Single.Solvers
                 DenseVector.Create(3, i => 4),
                 DenseVector.Create(3, i => 4),
                 DenseVector.Create(3, i => 4));
-            Assert.IsInstanceOf(typeof (CalculationRunning), iterator.Status, "Incorrect status");
+            Assert.AreEqual(IterationStatus.Running, iterator.Status, "Incorrect status");
 
             // Second step, should run out of iterations.
             iterator.DetermineStatus(
@@ -175,7 +108,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Single.Solvers
                 DenseVector.Create(3, i => 4),
                 DenseVector.Create(3, i => 4),
                 DenseVector.Create(3, i => 4));
-            Assert.IsInstanceOf(typeof (CalculationStoppedWithoutConvergence), iterator.Status, "Incorrect status");
+            Assert.AreEqual(IterationStatus.StoppedWithoutConvergence, iterator.Status, "Incorrect status");
         }
 
         /// <summary>
@@ -199,13 +132,13 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Single.Solvers
                 DenseVector.Create(3, i => 4),
                 DenseVector.Create(3, i => 4),
                 DenseVector.Create(3, i => 4));
-            Assert.IsInstanceOf(typeof (CalculationRunning), iterator.Status, "Incorrect status");
+            Assert.AreEqual(IterationStatus.Running, iterator.Status, "Incorrect status");
 
             iterator.Reset();
-            Assert.IsInstanceOf(typeof (CalculationIndetermined), iterator.Status, "Incorrect status");
-            Assert.IsInstanceOf(typeof (CalculationIndetermined), criteria[0].Status, "Incorrect status");
-            Assert.IsInstanceOf(typeof (CalculationIndetermined), criteria[1].Status, "Incorrect status");
-            Assert.IsInstanceOf(typeof (CalculationIndetermined), criteria[2].Status, "Incorrect status");
+            Assert.AreEqual(IterationStatus.Indetermined, iterator.Status, "Incorrect status");
+            Assert.AreEqual(IterationStatus.Indetermined, criteria[0].Status, "Incorrect status");
+            Assert.AreEqual(IterationStatus.Indetermined, criteria[1].Status, "Incorrect status");
+            Assert.AreEqual(IterationStatus.Indetermined, criteria[2].Status, "Incorrect status");
         }
     }
 }
diff --git a/src/UnitTests/LinearAlgebraTests/Single/Solvers/StopCriterium/DivergenceStopCriteriumTest.cs b/src/UnitTests/LinearAlgebraTests/Single/Solvers/StopCriterium/DivergenceStopCriteriumTest.cs
index fecd30c4..dfc24463 100644
--- a/src/UnitTests/LinearAlgebraTests/Single/Solvers/StopCriterium/DivergenceStopCriteriumTest.cs
+++ b/src/UnitTests/LinearAlgebraTests/Single/Solvers/StopCriterium/DivergenceStopCriteriumTest.cs
@@ -28,11 +28,11 @@
 // OTHER DEALINGS IN THE SOFTWARE.
 // </copyright>
 
+using System;
 using MathNet.Numerics.LinearAlgebra.Single;
 using MathNet.Numerics.LinearAlgebra.Single.Solvers.StopCriterium;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
+using MathNet.Numerics.LinearAlgebra.Solvers;
 using NUnit.Framework;
-using System;
 
 namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Single.Solvers.StopCriterium
 {
@@ -117,20 +117,6 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Single.Solvers.StopCrite
                 DenseVector.Create(3, i => 6)));
         }
 
-        /// <summary>
-        /// Determine status with <c>null</c> residual vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullResidualVectorThrowsArgumentNullException()
-        {
-            var criterium = new DivergenceStopCriterium(0.5, 15);
-            Assert.Throws<ArgumentNullException>(() => criterium.DetermineStatus(
-                1,
-                DenseVector.Create(3, i => 4),
-                DenseVector.Create(3, i => 5),
-                null));
-        }
-
         /// <summary>
         /// Can determine status with too few iterations.
         /// </summary>
@@ -151,7 +137,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Single.Solvers.StopCrite
                     new DenseVector(new[] {1.0f}),
                     new DenseVector(new[] {(i + 1)*(Increase + 0.1f)}));
 
-                Assert.IsInstanceOf(typeof (CalculationRunning), status, "Status check fail.");
+                Assert.AreEqual(IterationStatus.Running, status, "Status check fail.");
             }
         }
 
@@ -175,7 +161,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Single.Solvers.StopCrite
                     new DenseVector(new[] {1.0f}),
                     new DenseVector(new[] {(i + 1)*(Increase - 0.01f)}));
 
-                Assert.IsInstanceOf(typeof (CalculationRunning), status, "Status check fail.");
+                Assert.AreEqual(IterationStatus.Running, status, "Status check fail.");
             }
         }
 
@@ -199,7 +185,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Single.Solvers.StopCrite
                     new DenseVector(new[] {1.0f}),
                     new DenseVector(new[] {(i + 1)*(Increase - 0.01f)}));
 
-                Assert.IsInstanceOf(typeof (CalculationRunning), status, "Status check fail.");
+                Assert.AreEqual(IterationStatus.Running, status, "Status check fail.");
             }
 
             // Now make it fail by throwing in a NaN
@@ -209,7 +195,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Single.Solvers.StopCrite
                 new DenseVector(new[] {1.0f}),
                 new DenseVector(new[] {float.NaN}));
 
-            Assert.IsInstanceOf(typeof (CalculationDiverged), status2, "Status check fail.");
+            Assert.AreEqual(IterationStatus.Diverged, status2, "Status check fail.");
         }
 
         /// <summary>
@@ -234,7 +220,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Single.Solvers.StopCrite
                     new DenseVector(new[] {1.0f}),
                     new DenseVector(new[] {previous}));
 
-                Assert.IsInstanceOf(typeof (CalculationRunning), status, "Status check fail.");
+                Assert.AreEqual(IterationStatus.Running, status, "Status check fail.");
             }
 
             // Add the final residual. Now we should have divergence
@@ -245,7 +231,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Single.Solvers.StopCrite
                 new DenseVector(new[] {1.0f}),
                 new DenseVector(new[] {previous}));
 
-            Assert.IsInstanceOf(typeof (CalculationDiverged), status2, "Status check fail.");
+            Assert.AreEqual(IterationStatus.Diverged, status2, "Status check fail.");
         }
 
         /// <summary>
@@ -266,14 +252,14 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Single.Solvers.StopCrite
                 new DenseVector(new[] {1.0f}),
                 new DenseVector(new[] {float.NaN}));
 
-            Assert.IsInstanceOf(typeof (CalculationDiverged), status, "Status check fail.");
+            Assert.AreEqual(IterationStatus.Diverged, status, "Status check fail.");
 
             // Reset the state
             criterium.ResetToPrecalculationState();
 
             Assert.AreEqual(Increase, criterium.MaximumRelativeIncrease, "Incorrect maximum");
             Assert.AreEqual(Iterations, criterium.MinimumNumberOfIterations, "Incorrect iteration count");
-            Assert.IsInstanceOf(typeof (CalculationIndetermined), criterium.Status, "Status check fail.");
+            Assert.AreEqual(IterationStatus.Indetermined, criterium.Status, "Status check fail.");
         }
 
         /// <summary>
diff --git a/src/UnitTests/LinearAlgebraTests/Single/Solvers/StopCriterium/FailureStopCriteriumTest.cs b/src/UnitTests/LinearAlgebraTests/Single/Solvers/StopCriterium/FailureStopCriteriumTest.cs
index 58609468..7289b48f 100644
--- a/src/UnitTests/LinearAlgebraTests/Single/Solvers/StopCriterium/FailureStopCriteriumTest.cs
+++ b/src/UnitTests/LinearAlgebraTests/Single/Solvers/StopCriterium/FailureStopCriteriumTest.cs
@@ -30,7 +30,7 @@
 
 using MathNet.Numerics.LinearAlgebra.Single;
 using MathNet.Numerics.LinearAlgebra.Single.Solvers.StopCriterium;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
+using MathNet.Numerics.LinearAlgebra.Solvers;
 using NUnit.Framework;
 using System;
 
@@ -64,30 +64,6 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Single.Solvers.StopCrite
             Assert.Throws<ArgumentOutOfRangeException>(() => criterium.DetermineStatus(-1, DenseVector.Create(3, i => 4), DenseVector.Create(3, i => 5), DenseVector.Create(3, i => 6)));
         }
 
-        /// <summary>
-        /// Determine status with <c>null</c> solution vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullSolutionVectorThrowsArgumentNullException()
-        {
-            var criterium = new FailureStopCriterium();
-            Assert.IsNotNull(criterium, "There should be a criterium");
-
-            Assert.Throws<ArgumentNullException>(() => criterium.DetermineStatus(1, null, DenseVector.Create(3, i => 6), DenseVector.Create(4, i => 4)));
-        }
-
-        /// <summary>
-        /// Determine status with <c>null</c> residual vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullResidualVectorThrowsArgumentNullException()
-        {
-            var criterium = new FailureStopCriterium();
-            Assert.IsNotNull(criterium, "There should be a criterium");
-
-            Assert.Throws<ArgumentNullException>(() => criterium.DetermineStatus(1, DenseVector.Create(3, i => 4), DenseVector.Create(3, i => 6), null));
-        }
-
         /// <summary>
         /// Determine status with non-matching vectors throws <c>ArgumentException</c>.
         /// </summary>
@@ -114,7 +90,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Single.Solvers.StopCrite
             var residual = new DenseVector(new[] {1000, float.NaN, 2001});
 
             var status = criterium.DetermineStatus(5, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationFailure), status, "Should be failed");
+            Assert.AreEqual(IterationStatus.Failure, status, "Should be failed");
         }
 
         /// <summary>
@@ -131,7 +107,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Single.Solvers.StopCrite
             var residual = new DenseVector(new[] {1000.0f, 1000.0f, 2001.0f});
 
             var status = criterium.DetermineStatus(5, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationFailure), status, "Should be failed");
+            Assert.AreEqual(IterationStatus.Failure, status, "Should be failed");
         }
 
         /// <summary>
@@ -148,7 +124,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Single.Solvers.StopCrite
             var residual = new DenseVector(new[] {1.0f, 2.0f, 3.0f});
 
             var status = criterium.DetermineStatus(5, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationRunning), status, "Should be running");
+            Assert.AreEqual(IterationStatus.Running, status, "Should be running");
         }
 
         /// <summary>
@@ -165,10 +141,10 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Single.Solvers.StopCrite
             var residual = new DenseVector(new[] {1000.0f, 1000.0f, 2001.0f});
 
             var status = criterium.DetermineStatus(5, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationRunning), status, "Should be running");
+            Assert.AreEqual(IterationStatus.Running, status, "Should be running");
 
             criterium.ResetToPrecalculationState();
-            Assert.IsInstanceOf(typeof (CalculationIndetermined), criterium.Status, "Should not have started");
+            Assert.AreEqual(IterationStatus.Indetermined, criterium.Status, "Should not have started");
         }
 
         /// <summary>
diff --git a/src/UnitTests/LinearAlgebraTests/Single/Solvers/StopCriterium/IterationCountStopCriteriumTest.cs b/src/UnitTests/LinearAlgebraTests/Single/Solvers/StopCriterium/IterationCountStopCriteriumTest.cs
index 3abff679..51924ff8 100644
--- a/src/UnitTests/LinearAlgebraTests/Single/Solvers/StopCriterium/IterationCountStopCriteriumTest.cs
+++ b/src/UnitTests/LinearAlgebraTests/Single/Solvers/StopCriterium/IterationCountStopCriteriumTest.cs
@@ -31,7 +31,6 @@
 using System;
 using MathNet.Numerics.LinearAlgebra.Single;
 using MathNet.Numerics.LinearAlgebra.Solvers;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
 using NUnit.Framework;
 
 namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Single.Solvers.StopCriterium
@@ -98,10 +97,10 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Single.Solvers.StopCrite
             Assert.IsNotNull(criterium, "A criterium should have been created");
 
             var status = criterium.DetermineStatus(5, DenseVector.Create(3, i => 1), DenseVector.Create(3, i => 2), DenseVector.Create(3, i => 3));
-            Assert.IsInstanceOf(typeof (CalculationRunning), status, "Should be running");
+            Assert.AreEqual(IterationStatus.Running, status, "Should be running");
 
             var status2 = criterium.DetermineStatus(10, DenseVector.Create(3, i => 1), DenseVector.Create(3, i => 2), DenseVector.Create(3, i => 3));
-            Assert.IsInstanceOf(typeof (CalculationStoppedWithoutConvergence), status2, "Should be finished");
+            Assert.AreEqual(IterationStatus.StoppedWithoutConvergence, status2, "Should be finished");
         }
 
         /// <summary>
@@ -114,10 +113,10 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Single.Solvers.StopCrite
             Assert.IsNotNull(criterium, "A criterium should have been created");
 
             var status = criterium.DetermineStatus(5, DenseVector.Create(3, i => 1), DenseVector.Create(3, i => 2), DenseVector.Create(3, i => 3));
-            Assert.IsInstanceOf(typeof (CalculationRunning), status, "Should be running");
+            Assert.AreEqual(IterationStatus.Running, status, "Should be running");
 
             criterium.ResetToPrecalculationState();
-            Assert.IsInstanceOf(typeof (CalculationIndetermined), criterium.Status, "Should not have started");
+            Assert.AreEqual(IterationStatus.Indetermined, criterium.Status, "Should not have started");
         }
 
         /// <summary>
diff --git a/src/UnitTests/LinearAlgebraTests/Single/Solvers/StopCriterium/ResidualStopCriteriumTest.cs b/src/UnitTests/LinearAlgebraTests/Single/Solvers/StopCriterium/ResidualStopCriteriumTest.cs
index 00cf9771..f3955bee 100644
--- a/src/UnitTests/LinearAlgebraTests/Single/Solvers/StopCriterium/ResidualStopCriteriumTest.cs
+++ b/src/UnitTests/LinearAlgebraTests/Single/Solvers/StopCriterium/ResidualStopCriteriumTest.cs
@@ -28,11 +28,11 @@
 // OTHER DEALINGS IN THE SOFTWARE.
 // </copyright>
 
+using System;
 using MathNet.Numerics.LinearAlgebra.Single;
 using MathNet.Numerics.LinearAlgebra.Single.Solvers.StopCriterium;
-using MathNet.Numerics.LinearAlgebra.Solvers.Status;
+using MathNet.Numerics.LinearAlgebra.Solvers;
 using NUnit.Framework;
-using System;
 
 namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Single.Solvers.StopCriterium
 {
@@ -115,54 +115,6 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Single.Solvers.StopCrite
                 DenseVector.Create(3, i => 6)));
         }
 
-        /// <summary>
-        /// Determine status with <c>null</c> solution vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullSolutionVectorThrowsArgumentNullException()
-        {
-            var criterium = new ResidualStopCriterium(1e-6f, 50);
-            Assert.IsNotNull(criterium, "There should be a criterium");
-
-            Assert.Throws<ArgumentNullException>(() => criterium.DetermineStatus(
-                1,
-                null,
-                DenseVector.Create(3, i => 5),
-                DenseVector.Create(3, i => 6)));
-        }
-
-        /// <summary>
-        /// Determine status with <c>null</c> source vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullSourceVectorThrowsArgumentNullException()
-        {
-            var criterium = new ResidualStopCriterium(1e-6f, 50);
-            Assert.IsNotNull(criterium, "There should be a criterium");
-
-            Assert.Throws<ArgumentNullException>(() => criterium.DetermineStatus(
-                1,
-                DenseVector.Create(3, i => 4),
-                null,
-                DenseVector.Create(3, i => 6)));
-        }
-
-        /// <summary>
-        /// Determine status with <c>null</c> residual vector throws <c>ArgumentNullException</c>.
-        /// </summary>
-        [Test]
-        public void DetermineStatusWithNullResidualVectorThrowsArgumentNullException()
-        {
-            var criterium = new ResidualStopCriterium(1e-6f, 50);
-            Assert.IsNotNull(criterium, "There should be a criterium");
-
-            Assert.Throws<ArgumentNullException>(() => criterium.DetermineStatus(
-                1,
-                DenseVector.Create(3, i => 4),
-                DenseVector.Create(3, i => 5),
-                null));
-        }
-
         /// <summary>
         /// Determine status with non-matching solution vector throws <c>ArgumentException</c>.
         /// </summary>
@@ -225,7 +177,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Single.Solvers.StopCrite
             var residual = new DenseVector(new[] {1000.0f, 1000.0f, 2001.0f});
 
             var status = criterium.DetermineStatus(5, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationDiverged), status, "Should be diverged");
+            Assert.AreEqual(IterationStatus.Diverged, status, "Should be diverged");
         }
 
         /// <summary>
@@ -242,7 +194,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Single.Solvers.StopCrite
             var residual = new DenseVector(new[] {1000.0f, float.NaN, 2001.0f});
 
             var status = criterium.DetermineStatus(5, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationDiverged), status, "Should be diverged");
+            Assert.AreEqual(IterationStatus.Diverged, status, "Should be diverged");
         }
 
         /// <summary>
@@ -259,7 +211,7 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Single.Solvers.StopCrite
             var residual = new DenseVector(new[] {0.0f, 0.0f, 0.0f});
 
             var status = criterium.DetermineStatus(0, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationConverged), status, "Should be done");
+            Assert.AreEqual(IterationStatus.Converged, status, "Should be done");
         }
 
         /// <summary>
@@ -281,10 +233,10 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Single.Solvers.StopCrite
             var residual = new DenseVector(new[] {0.001f, 0.001f, 0.002f});
 
             var status = criterium.DetermineStatus(5, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationRunning), status, "Should still be running");
+            Assert.AreEqual(IterationStatus.Running, status, "Should still be running");
 
             var status2 = criterium.DetermineStatus(16, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationConverged), status2, "Should be done");
+            Assert.AreEqual(IterationStatus.Converged, status2, "Should be done");
         }
 
         /// <summary>
@@ -301,10 +253,10 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Single.Solvers.StopCrite
             var residual = new DenseVector(new[] {1.000f, 1.000f, 2.001f});
 
             var status = criterium.DetermineStatus(5, solution, source, residual);
-            Assert.IsInstanceOf(typeof (CalculationRunning), status, "Should be running");
+            Assert.AreEqual(IterationStatus.Running, status, "Should be running");
 
             criterium.ResetToPrecalculationState();
-            Assert.IsInstanceOf(typeof (CalculationIndetermined), criterium.Status, "Should not have started");
+            Assert.AreEqual(IterationStatus.Indetermined, criterium.Status, "Should not have started");
         }
 
         /// <summary>