Routine Name: matrixMatrixProduct

Author: Christopher Johnson

Language: C++11. Tested with g++ compiler.

Declared in “matrix.h”

Description/Purpose: Performs Matrix-Matrix multiplication.

Input: Matrix a and Matrix b, where Matrix is a typedef of std::vector<std::vector<double>>.

Output: Returns a Matrix, typedef of std::vector<std::vector<double>>. The size is equal rows(a) x cols(b).

Usage/Example:

Two Matrices must first be defined, and then the method may be called.

Matrix c = { {1,2,3},{4,5,6} };
Matrix d = { {7,8},{9,10},{11,12} };
std::cout << "C * D is\n"
printVector(matrixMatrixProduct(c,d));

Output from the lines above:

C * D is
[[58,64],
[139,154]]

Implementation/Code: The following is the code for matrixMatrixProduct(a,b)

Matrix matrixMatrixProduct(Matrix a, Matrix b)
{
    int n = a.size();
int m = b.size();
int r = b[0].size();

    Matrix sol(n, Vector(r,0));

    for(int i=0;i<n;++i)
    for(int j=0;j<r;++j)
        for(int k=0;k<m;++k)
        sol[i][j]+=a[i][k]*b[k][j];
    return sol;
}

Last Modified: October/2017