Sparse Linear Algebra: minor add/subtract optimization, gh-18.

src/Numerics/LinearAlgebra/Complex/SparseVector.cs

@@ -430,7 +430,6 @@ namespace MathNet.Numerics.LinearAlgebra.Complex
                     }
                     else if (j >= otherSparse.NonZerosCount || i < NonZerosCount && _nonZeroIndices[i] < otherSparse._nonZeroIndices[j])
                     {
-                        _nonZeroValues[i] += otherSparse.At(_nonZeroIndices[i]);
                         i++;
                     }
                     else
@@ -577,7 +576,6 @@ namespace MathNet.Numerics.LinearAlgebra.Complex
                     }
                     else if (j >= otherSparse.NonZerosCount || i < NonZerosCount && _nonZeroIndices[i] < otherSparse._nonZeroIndices[j])
                     {
-                        _nonZeroValues[i] -= otherSparse.At(_nonZeroIndices[i]);
                         i++;
                     }
                     else

src/Numerics/LinearAlgebra/Complex32/SparseVector.cs

@@ -460,7 +460,6 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32
                     }
                     else if (j >= otherSparse.NonZerosCount || i < NonZerosCount && _nonZeroIndices[i] < otherSparse._nonZeroIndices[j])
                     {
-                        _nonZeroValues[i] += otherSparse.At(_nonZeroIndices[i]);
                         i++;
                     }
                     else
@@ -607,7 +606,6 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32
                     }
                     else if (j >= otherSparse.NonZerosCount || i < NonZerosCount && _nonZeroIndices[i] < otherSparse._nonZeroIndices[j])
                     {
-                        _nonZeroValues[i] -= otherSparse.At(_nonZeroIndices[i]);
                         i++;
                     }
                     else

src/Numerics/LinearAlgebra/Double/SparseVector.cs

@@ -378,7 +378,6 @@ namespace MathNet.Numerics.LinearAlgebra.Double
                     }
                     else if (j >= otherSparse.NonZerosCount || i < NonZerosCount && _nonZeroIndices[i] < otherSparse._nonZeroIndices[j])
                     {
-                        _nonZeroValues[i] += otherSparse.At(_nonZeroIndices[i]);
                         i++;
                     }
                     else
@@ -525,7 +524,6 @@ namespace MathNet.Numerics.LinearAlgebra.Double
                     }
                     else if (j >= otherSparse.NonZerosCount || i < NonZerosCount && _nonZeroIndices[i] < otherSparse._nonZeroIndices[j])
                     {
-                        _nonZeroValues[i] -= otherSparse.At(_nonZeroIndices[i]);
                         i++;
                     }
                     else

src/Numerics/LinearAlgebra/Single/SparseVector.cs

@@ -408,7 +408,6 @@ namespace MathNet.Numerics.LinearAlgebra.Single
                     }
                     else if (j >= otherSparse.NonZerosCount || i < NonZerosCount && _nonZeroIndices[i] < otherSparse._nonZeroIndices[j])
                     {
-                        _nonZeroValues[i] += otherSparse.At(_nonZeroIndices[i]);
                         i++;
                     }
                     else
@@ -555,7 +554,6 @@ namespace MathNet.Numerics.LinearAlgebra.Single
                     }
                     else if (j >= otherSparse.NonZerosCount || i < NonZerosCount && _nonZeroIndices[i] < otherSparse._nonZeroIndices[j])
                     {
-                        _nonZeroValues[i] -= otherSparse.At(_nonZeroIndices[i]);
                         i++;
                     }
                     else