Fixed Add and Subtract methods in DiagonalMatrix to use the correct type of matrix.

src/Numerics/LinearAlgebra/Complex/DiagonalMatrix.cs

@@ -301,11 +301,11 @@ namespace MathNet.Numerics.LinearAlgebra.Complex
             Matrix<Complex> result;
             if (other is DiagonalMatrix)
             {
-                result = new DenseMatrix(RowCount, ColumnCount);
+                result = new DiagonalMatrix(RowCount, ColumnCount);
             }
             else
             {
-                result = new DiagonalMatrix(RowCount, ColumnCount);
+                result = new DenseMatrix(RowCount, ColumnCount);
             }
 
             Add(other, result);

src/Numerics/LinearAlgebra/Complex32/DiagonalMatrix.cs

@@ -306,11 +306,11 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32
             Matrix<Complex32> result;
             if (other is DiagonalMatrix)
             {
-                result = new DenseMatrix(RowCount, ColumnCount);
+                result = new DiagonalMatrix(RowCount, ColumnCount);
             }
             else
             {
-                result = new DiagonalMatrix(RowCount, ColumnCount);
+                result = new DenseMatrix(RowCount, ColumnCount);
             }
 
             Add(other, result);
@@ -381,11 +381,11 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32
             Matrix<Complex32> result;
             if (other is DiagonalMatrix)
             {
-                result = new DenseMatrix(RowCount, ColumnCount);
+                result = new DiagonalMatrix(RowCount, ColumnCount);
             }
             else
             {
-                result = new DiagonalMatrix(RowCount, ColumnCount);
+                result = new DenseMatrix(RowCount, ColumnCount);
             }
 
             Subtract(other, result);

src/Numerics/LinearAlgebra/Double/DiagonalMatrix.cs

@@ -300,11 +300,11 @@ namespace MathNet.Numerics.LinearAlgebra.Double
             Matrix<double> result;
             if (other is DiagonalMatrix)
             {
-                result = new DenseMatrix(RowCount, ColumnCount);
+                result = new DiagonalMatrix(RowCount, ColumnCount);
             }
             else
             {
-                result = new DiagonalMatrix(RowCount, ColumnCount);
+                result = new DenseMatrix(RowCount, ColumnCount);
             }
 
             Add(other, result);
@@ -375,11 +375,11 @@ namespace MathNet.Numerics.LinearAlgebra.Double
             Matrix<double> result;
             if (other is DiagonalMatrix)
             {
-                result = new DenseMatrix(RowCount, ColumnCount);
+                result = new DiagonalMatrix(RowCount, ColumnCount);
             }
             else
             {
-                result = new DiagonalMatrix(RowCount, ColumnCount);
+                result = new DenseMatrix(RowCount, ColumnCount);
             }
 
             Subtract(other, result);

src/Numerics/LinearAlgebra/Single/DiagonalMatrix.cs

@@ -300,11 +300,11 @@ namespace MathNet.Numerics.LinearAlgebra.Single
             Matrix<float> result;
             if (other is DiagonalMatrix)
             {
-                result = new DenseMatrix(RowCount, ColumnCount);
+                result = new DiagonalMatrix(RowCount, ColumnCount);
             }
             else
             {
-                result = new DiagonalMatrix(RowCount, ColumnCount);
+                result = new DenseMatrix(RowCount, ColumnCount);
             }
 
             Add(other, result);
@@ -375,11 +375,11 @@ namespace MathNet.Numerics.LinearAlgebra.Single
             Matrix<float> result;
             if (other is DiagonalMatrix)
             {
-                result = new DenseMatrix(RowCount, ColumnCount);
+                result = new DiagonalMatrix(RowCount, ColumnCount);
             }
             else
             {
-                result = new DiagonalMatrix(RowCount, ColumnCount);
+                result = new DenseMatrix(RowCount, ColumnCount);
             }
 
             Subtract(other, result);