matrix mult general

t13e10.multMat.cpp

// t13e10.multMat.cpp
// juanfc 2023-11-23
// https://gist.github.com/37aac4e61e052185136417c9a3f071d9

#include <iostream>
#include <array>
using namespace std;

const int K = 5;
const int M = 4;
const int N = 3;
typedef array<array<int, M>,N> TMatNm;
typedef array<array<int, K>,M> TMatmK;
typedef array<array<int, K>,N> TMatNK;


int main()
{
    TMatNK mult(TMatNm, TMatmK);
    void printMat(TMatNm);
    void printMat(TMatmK);
    void printMat(TMatNK);

    TMatNm a = {{
        {{1, 2, 3, 4}},
        {{1, 2, 3, 4}},
        {{1, 2, 3, 4}}
    }};
    TMatmK b = {{
        {{1, 0, 0, 0, 0}},
        {{0, 1, 0, 0, 0}},
        {{0, 0, 1, 0, 0}},
        {{0, 0, 0, 1, 0}}
    }};
    cout << "a: " << endl;
    printMat(a);
    cout << "b: " << endl;
    printMat(b);
    cout << "a x b: " << endl;
    printMat(mult(a, b));

    return 0;
}

TMatNK mult(TMatNm a, TMatmK b)
{
    TMatNK res;
    for (int r = 0; r < N; ++r)
        for (int c = 0; c < K; ++c) {
            res[r][c] = 0;
            for (int i = 0; i < M; ++i)
                res[r][c] += a[r][i] * b[i][c];
        }
    return res;
}


void printMat(TMatNm m)
{
    for (int i = 0; i < N; ++i) {
        for (int j = 0; j < M; ++j)
            cout << m[i][j] << " ";
        cout << endl;
    }
    cout << endl;
}

void printMat(TMatmK m)
{
    for (int i = 0; i < M; ++i) {
        for (int j = 0; j < K; ++j)
            cout << m[i][j] << " ";
        cout << endl;
    }
    cout << endl;
}

void printMat(TMatNK m)
{
    for (int i = 0; i < N; ++i) {
        for (int j = 0; j < K; ++j)
            cout << m[i][j] << " ";
        cout << endl;
    }
    cout << endl;
}