C# Matrix*Vector = DotProduct Using MathNet Library

Question

I am currently building a FeedForward Neural Network library on C# and am struggling with matrix multiplication.

To those who are familiar with MathNet library; is there an existing function where it can take a Matrix and Vector (or versa) and return a Scalar as dot product?

Thanks in advance.

Answer 1

You are correct, there doesn't seem to be an existing function for it. You can use the following:

double dotproduct = 0;
for (i = 0; i <= m.ColumnCount; i++) {
    dotproduct += m.Column(i).DotProduct(v);
}

Answer 2

A solution to dot product two vectors in MathNet (was not able to figure out how to do it with a matrix)

Install MathNet.Spatial nuget

using MathNet.Spatial.Euclidean;

---

Then...

The Vector3D struct comes from the spatial ecluidian namespace

Answer 3

the * operator between two vector objects in mat.net.numerics is their dot product.

Also, if you multiply an mxn matrix with a vector of length n, you get the scalar dot product results of each row of the matrix with the vector in the as a vector in the output.