Multiply 2 matrices in Javascript

Question

I\'m doing a function that multiplies 2 matrices. The matrices will always have the same number of rows and columns. (2x2, 5x5, 23x23, ...)

When I print it, it doesn

Answer 1

This version stores rows as temporaries thus reducing the effective amount of index lookups. By this benchmark the achieved performance is almost 2 times faster if compared to the version withou storing rows.

function multiply(a, b) {
    let aRows = a.length;
    let aCols = a[0].length;
    let bCols = b[0].length;
    let result = new Array(aRows); 
    for (let r = 0; r < aRows; ++r) {
        const row = new Array(bCols);
        result[r] = row;
        const ar = a[r];
        for (let c = 0; c < bCols; ++c) {
            let sum = 0.;     
            for (let i = 0; i < aCols; ++i) {
                sum += ar[i] * b[i][c];
            }
            row[c] = sum;  
        }
    }
    return result;
}

const m = multiply(
        [[8, 3], [2, 4], [3, 6]],
        [[1, 2, 3], [4, 6, 8]]
    );
console.log(m);
function display(m) {
    for (var r = 0; r < m.length; ++r) {
        document.write('  '+m[r].join(' ')+'
');
    }
}

var a = [[8, 3], [2, 4], [3, 6]],
    b = [[1, 2, 3], [4, 6, 8]];
document.write('matrix a:
');
display(a);
document.write('matrix b:
');
display(b);
document.write('a * b =
');
display(multiply(a, b));