Added Matrix.Clear method.

src/Numerics/LinearAlgebra/Double/DenseMatrix.cs

@@ -182,6 +182,14 @@ namespace MathNet.Numerics.LinearAlgebra.Double
             Data[column * RowCount + row] = value;
         }
 
+        /// <summary>
+        /// Sets all values to zero.
+        /// </summary>
+        public override void Clear()
+        {
+            Array.Clear(Data, 0, Data.Length);
+        }
+
         #region Elementary operations
         /// <summary>
         /// Adds another matrix to this matrix. The result will be written into this matrix.

src/Numerics/LinearAlgebra/Double/Matrix.cs

@@ -412,6 +412,20 @@ namespace MathNet.Numerics.LinearAlgebra.Double
         }
 
         #endregion
+
+        /// <summary>
+        /// Sets all values to zero.
+        /// </summary>
+        public virtual void Clear()
+        {
+            for (int i = 0; i < RowCount; i++)
+            {
+                for (int j = 0; j < ColumnCount; j++)
+                {
+                    At(i, j, 0);
+                }
+            }
+        }
         
         #region Elementary operations
         /// <summary>

src/UnitTests/LinearAlgebraTests/Double/MatrixTests.cs

@@ -162,6 +162,20 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double
         {
         }
 
+        [Test]
+        public void CanClearMatrix()
+        {
+            Matrix matrix = (Matrix) testMatrices["Singular3x3"].Clone();
+            matrix.Clear();
+            for (int i = 0; i < matrix.RowCount; i++)
+            {
+                for (int j = 0; j < matrix.ColumnCount; j++)
+                {
+                    Assert.AreEqual(0, matrix[i, j]);
+                }
+            }
+        }
+
         #region Elementary operations
         [Test]
         [Row("Singular3x3", "Square3x3")]