How to multiply matrices of different sizes?-CodePudding

I am trying to multiply matrices of different sizes. Generally if the matrix has the same size you would use 2 for loops, but what about matrices with different sizes?

int main(int argc, char const *argv[]) {
  int mat1[2][3] ={{1,2,3},
                  {4,5,6},
                  };
  int mat2[3][2] = {{1,2},
                    {3,4},
                    {6,5}
                   };

int *pointerToMat1 = &mat1[0][0];
int *pointerToMat2 = &mat2[0][0];



  return 0;
}

I was thinking to use pointers but I got lost. The above example is just to test the function, in general matrixProduct should work for any size matrices, as long as mathematical rules hold.

CodePudding user response：

Well.. The formula for matrix multiplication is pretty straightforward:

Multiplying A(MxN) and B(NxM) gives C(MxM):

C[i,j] = sum ( A[i,k]*B[k,j] k = 0..N ) ; i,j=0..M

So with your code I would do:

#include <stdio.h>

int main()
{
      int mat1[2][3] ={{1,2,3},
                  {4,5,6},
                  };
      int mat2[3][2] = {{1,2},
                        {3,4},
                        {6,5}
                       };
    
    int *pointerToMat1 = &mat1[0][0];
    int *pointerToMat2 = &mat2[0][0];
    
    
    int C[2][2];
    for ( int i=0; i<2; i  ) {
        for( int j=0;j<2;j   ) {
           C[i][j] = 0;
           for( int k=0;k<3;k   ) {
               printf("%dx%d=%d\n",mat1[i][k],mat2[k][j],mat1[i][k]*mat2[k][j]);
              C[i][j]  = mat1[i][k]*mat2[k][j];
           } 
        }
    }
    
    printf("%d %d %d %d",C[0][0],C[0][1],C[1][0],C[1][1]);
    
}