chroma-js/src/utils/multiply-matrices.js

JavaScript library for color conversions

// from https://www.w3.org/TR/css-color-4/multiply-matrices.js
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) => {
            if (!Array.isArray(row)) {
                return col.reduce((a, c) => a + c * row, 0);
            }

            return row.reduce((a, c, i) => a + c * (col[i] || 0), 0);
        })
    );

    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;
}