colorjs.io/src/multiply-matrices.js

Let’s get serious about color

// A is m x n. B is n x p. product is m x p.
export default function multiplyMatrices(A, B) {
	let m = A.length;

	if (!Array.isArray(A[0])) {
		// A is vector, convert to [[a, b, c, ...]]
		A = [A];
	}

	if (!Array.isArray(B[0])) {
		// B is vector, convert to [[a], [b], [c], ...]]
		B = B.map(x => [x]);
	}

	let p = B[0].length;
	let B_cols = B[0].map((_, i) => B.map(x => x[i])); // transpose B
	let product = A.map(row => B_cols.map(col => {
		let ret = 0;

		if (!Array.isArray(row)) {
			for (let c of col) {
				ret += row * c;
			}

			return ret;
		}

		for (let i=0; i < row.length; i++) {
			ret += row[i] * (col[i] || 0);
		}

		return ret;
	}));

	if (m === 1) {
		product = product[0]; // Avoid [[a, b, c, ...]]
	}

	if (p === 1) {
		return product.map(x => x[0]); // Avoid [[a], [b], [c], ...]]
	}

	return product;
}