dot.cpp

vector <float> dot (const vector <float>& m1, const vector <float>& m2, 
                    const int m1_rows, const int m1_columns, const int m2_columns) {
    
    /*  Returns the product of two matrices: m1 x m2.
        Inputs:
            m1: vector, left matrix of size m1_rows x m1_columns
            m2: vector, right matrix of size m1_columns x m2_columns 
                (the number of rows in the right matrix must be equal 
                to the number of the columns in the left one)
            m1_rows: int, number of rows in the left matrix m1
            m1_columns: int, number of columns in the left matrix m1
            m2_columns: int, number of columns in the right matrix m2
        Output: vector, m1 * m2, product of two vectors m1 and m2, 
                a matrix of size m1_rows x m2_columns
    */
    
    vector <float> output (m1_rows*m2_columns);
    
    for( int row = 0; row != m1_rows; ++row ) {
        for( int col = 0; col != m2_columns; ++col ) {
            output[ row * m2_columns + col ] = 0.f;
            for( int k = 0; k != m1_columns; ++k ) {
                output[ row * m2_columns + col ] += m1[ row * m1_columns + k ] * m2[ k * m2_columns + col ];
            }
        }
    }
    
    return output;
}