LA: diagonal matrix mult should choose sensible result storage

src/Numerics/LinearAlgebra/Complex/DiagonalMatrix.cs

@@ -607,13 +607,7 @@ namespace MathNet.Numerics.LinearAlgebra.Complex
                 throw DimensionsDontMatch<ArgumentException>(this, other);
             }
 
-            var m = other as DiagonalMatrix;
-            if (m == null)
-            {
-                return base.Multiply(other);
-            }
-
-            var result = (DiagonalMatrix)CreateMatrix(RowCount, other.ColumnCount);
+            var result = other.CreateMatrix(RowCount, other.ColumnCount);
             Multiply(other, result);
             return result;
         }
@@ -788,7 +782,7 @@ namespace MathNet.Numerics.LinearAlgebra.Complex
                 throw DimensionsDontMatch<ArgumentException>(this, otherDiagonal);
             }
 
-            var result = (DiagonalMatrix)CreateMatrix(RowCount, other.RowCount);
+            var result = other.CreateMatrix(RowCount, other.RowCount);
             TransposeAndMultiply(other, result);
             return result;
         }

src/Numerics/LinearAlgebra/Complex32/DiagonalMatrix.cs

@@ -612,13 +612,7 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32
                 throw DimensionsDontMatch<ArgumentException>(this, other);
             }
 
-            var m = other as DiagonalMatrix;
-            if (m == null)
-            {
-                return base.Multiply(other);
-            }
-
-            var result = (DiagonalMatrix)CreateMatrix(RowCount, other.ColumnCount);
+            var result = other.CreateMatrix(RowCount, other.ColumnCount);
             Multiply(other, result);
             return result;
         }
@@ -793,7 +787,7 @@ namespace MathNet.Numerics.LinearAlgebra.Complex32
                 throw DimensionsDontMatch<ArgumentException>(this, otherDiagonal);
             }
 
-            var result = (DiagonalMatrix)CreateMatrix(RowCount, other.RowCount);
+            var result = other.CreateMatrix(RowCount, other.RowCount);
             TransposeAndMultiply(other, result);
             return result;
         }

src/Numerics/LinearAlgebra/Double/DiagonalMatrix.cs

@@ -601,13 +601,7 @@ namespace MathNet.Numerics.LinearAlgebra.Double
                 throw DimensionsDontMatch<ArgumentException>(this, other);
             }
 
-            var m = other as DiagonalMatrix;
-            if (m == null)
-            {
-                return base.Multiply(other);
-            }
-
-            var result = (DiagonalMatrix)CreateMatrix(RowCount, other.ColumnCount);
+            var result = other.CreateMatrix(RowCount, other.ColumnCount);
             Multiply(other, result);
             return result;
         }
@@ -782,7 +776,7 @@ namespace MathNet.Numerics.LinearAlgebra.Double
                 throw DimensionsDontMatch<ArgumentException>(this, otherDiagonal);
             }
 
-            var result = (DiagonalMatrix)CreateMatrix(RowCount, other.RowCount);
+            var result = other.CreateMatrix(RowCount, other.RowCount);
             TransposeAndMultiply(other, result);
             return result;
         }

src/Numerics/LinearAlgebra/Single/DiagonalMatrix.cs

@@ -606,13 +606,7 @@ namespace MathNet.Numerics.LinearAlgebra.Single
                 throw DimensionsDontMatch<ArgumentException>(this, other);
             }
 
-            var m = other as DiagonalMatrix;
-            if (m == null)
-            {
-                return base.Multiply(other);
-            }
-
-            var result = (DiagonalMatrix)CreateMatrix(RowCount, other.ColumnCount);
+            var result = other.CreateMatrix(RowCount, other.ColumnCount);
             Multiply(other, result);
             return result;
         }
@@ -787,7 +781,7 @@ namespace MathNet.Numerics.LinearAlgebra.Single
                 throw DimensionsDontMatch<ArgumentException>(this, otherDiagonal);
             }
 
-            var result = (DiagonalMatrix)CreateMatrix(RowCount, other.RowCount);
+            var result = other.CreateMatrix(RowCount, other.RowCount);
             TransposeAndMultiply(other, result);
             return result;
         }

src/UnitTests/LinearAlgebraTests/Double/DiagonalMatrixTests.cs

@@ -665,5 +665,14 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double
             var subM3 = diagMatrix.SubMatrix(0, 3, 1, 2);
             Assert.IsTrue(subM3.Equals(new DenseMatrix(3, 2, new[] { 0d, 2d, 0d, 0d, 0d, 3d })));
         }
+
+        [Test]
+        public void DiagonalDenseMatrixMultiplication_IssueCP5706()
+        {
+            Matrix<double> diagonal = DiagonalMatrix.Identity(3);
+            Matrix<double> dense = new DenseMatrix(new double[,] { { 1, 2, 3 }, { 1, 2, 3 }, { 1, 2, 3 } });
+            var test = diagonal * dense;
+            var test2 = dense * diagonal;
+        }
     }
 }