Implemented DoTranspsoeThisAndMultiply for vectors on Double.

src/Numerics/LinearAlgebra/Double/DenseMatrix.cs

@@ -444,6 +444,47 @@ namespace MathNet.Numerics.LinearAlgebra.Double
             }
         }
 
+        /// <summary>
+        /// Multiplies the transpose of this matrix with a vector and places the results into the result vector.
+        /// </summary>
+        /// <param name="rightSide">The vector to multiply with.</param>
+        /// <param name="result">The result of the multiplication.</param>
+        protected override void DoTransposeThisAndMultiply(Vector<double> rightSide, Vector<double> result)
+        {
+            var denseRight = rightSide as DenseVector;
+            var denseResult = result as DenseVector;
+
+            if (denseRight == null || denseResult == null)
+            {
+                base.DoTransposeThisAndMultiply(rightSide, result);
+            }
+            else
+            {
+                Control.LinearAlgebraProvider.MatrixMultiplyWithUpdate(
+                    Algorithms.LinearAlgebra.Transpose.DontTranspose,
+                    Algorithms.LinearAlgebra.Transpose.DontTranspose,
+                    1.0,
+                    Data,
+                    RowCount,
+                    ColumnCount,
+                    denseRight.Data,
+                    denseRight.Count,
+                    1,
+                    0.0,
+                    denseResult.Data);
+            }
+        }
+
+        /// <summary>
+        /// Multiplies the transpose of this matrix with another matrix and places the results into the result matrix.
+        /// </summary>
+        /// <param name="other">The matrix to multiply with.</param>
+        /// <param name="result">The result of the multiplication.</param>
+        protected override void DoTransposeThisAndMultiply(Matrix<double> other, Matrix<double> result)
+        {
+            throw new NotImplementedException();
+        }
+
         /// <summary>
         /// Negate each element of this matrix and place the results into the result matrix.
         /// </summary>

src/Numerics/LinearAlgebra/Double/Matrix.cs

@@ -269,6 +269,24 @@ namespace MathNet.Numerics.LinearAlgebra.Double
             }
         }
 
+        /// <summary>
+        /// Multiplies the transpose of this matrix with a vector and places the results into the result vector.
+        /// </summary>
+        /// <param name="rightSide">The vector to multiply with.</param>
+        /// <param name="result">The result of the multiplication.</param>
+        protected override void DoTransposeThisAndMultiply(Vector<double> rightSide, Vector<double> result)
+        {
+            for (var i = 0; i < ColumnCount; i++)
+            {
+                var s = 0.0;
+                for (var j = 0; j != RowCount; j++)
+                {
+                    s += At(j, i) * rightSide[j];
+                }
+                result[i] = s;
+            }
+        }
+
         /// <summary>
         /// Negate each element of this matrix and place the results into the result matrix.
         /// </summary>