Matrix multiplication with scalar.

src/Numerics/LinearAlgebra/Double/Matrix.Arithmetic.cs

@@ -38,6 +38,57 @@ namespace MathNet.Numerics.LinearAlgebra.Double
     /// </summary>
     public abstract partial class Matrix
     {
+        /// <summary>
+        /// Multiplies each element of this matrix with a scalar.
+        /// </summary>
+        /// <param name="scalar">The scalar to multiply with.</param>
+        public virtual void Multiply(double scalar)
+        {
+            if (Precision.AlmostEqualInDecimalPlaces(1.0, scalar, 15))
+            {
+                return;
+            }
+
+            Parallel.For(
+                0,
+                RowCount,
+                i =>
+                {
+                    for (int j = 0; j < ColumnCount; j++)
+                    {
+                        At(i, j, At(i, j) * scalar);
+                    }
+                });
+        }
+
+        /// <summary>
+        /// Multiplies each element of the matrix by a scalar and places results into the result matrix.
+        /// </summary>
+        /// <param name="scalar">The scalar to multiply the matrix with.</param>
+        /// <param name="result">The matrix to multiply.</param>
+        /// <exception cref="ArgumentNullException">If the result matrix is <see langword="null" />.</exception> 
+        /// <exception cref="ArgumentException">If the result matrix's dimensions are not the same as this matrix.</exception>
+        public virtual void Multiply(double scalar, Matrix result)
+        {
+            if (result == null)
+            {
+                throw new ArgumentNullException("result");
+            }
+
+            if (result.RowCount != RowCount)
+            {
+                throw new ArgumentException("result", Resources.ArgumentMatrixSameRowDimension);
+            }
+
+            if (result.ColumnCount != ColumnCount)
+            {
+                throw new ArgumentException("result", Resources.ArgumentMatrixSameColumnDimension);
+            }
+
+            CopyTo(result);
+            result.Multiply(scalar);
+        }
+
         /// <summary>
         /// Adds another matrix to this matrix. The result will be written into this matrix.
         /// </summary>

src/UnitTests/LinearAlgebraTests/Double/MatrixTests.Arithmetic.cs

@@ -8,6 +8,73 @@ namespace MathNet.Numerics.UnitTests.LinearAlgebraTests.Double
 {
     public abstract partial class MatrixTests
     {
+        [Test]
+        [Row(0)]
+        [Row(1)]
+        [Row(2.2)]
+        [MultipleAsserts]
+        public void CanMultiplyWithScalar(double scalar)
+        {
+            var matrix = testMatrices["Singular3x3"];
+            var clone = matrix.Clone();
+            clone.Multiply(scalar);
+
+            for (int i = 0; i < matrix.RowCount; i++)
+            {
+                for (int j = 0; j < matrix.ColumnCount; j++)
+                {
+                    Assert.AreEqual(matrix[i, j] * scalar, clone[i, j]);
+                }
+            }
+        }
+
+        [Test]
+        [Row(0)]
+        [Row(1)]
+        [Row(2.2)]
+        [MultipleAsserts]
+        public void CanMultiplyWithScalarIntoResult(double scalar)
+        {
+            var matrix = testMatrices["Singular3x3"];
+            var result = matrix.Clone();
+            matrix.Multiply(scalar, result);
+
+            for (int i = 0; i < matrix.RowCount; i++)
+            {
+                for (int j = 0; j < matrix.ColumnCount; j++)
+                {
+                    Assert.AreEqual(matrix[i, j] * scalar, result[i, j]);
+                }
+            }
+        }
+
+        [Test]
+        [ExpectedException(typeof(ArgumentNullException))]
+        public void MultiplyWithScalarIntoResultFailsWhenResultIsNull()
+        {
+            var matrix = testMatrices["Singular3x3"];
+            Matrix result = null;
+            matrix.Multiply(2.3, result);
+        }
+
+        [Test]
+        [ExpectedArgumentException]
+        public void MultiplyWithScalarFailsWhenResultHasMoreRows()
+        {
+            var matrix = testMatrices["Singular3x3"];
+            Matrix result = CreateMatrix(matrix.RowCount + 1, matrix.ColumnCount);
+            matrix.Multiply(2.3, result);
+        }
+
+        [Test]
+        [ExpectedArgumentException]
+        public void MultiplyWithScalarFailsWhenResultHasMoreColumns()
+        {
+            var matrix = testMatrices["Singular3x3"];
+            Matrix result = CreateMatrix(matrix.RowCount, matrix.ColumnCount + 1);
+            matrix.Multiply(2.3, result);
+        }
+
         [Test]
         [Row("Singular3x3", "Square3x3")]
         [Row("Singular4x4", "Square4x4")]