@vect/matrix-algebra/index.js

An array util tool

import { draft } from '@vect/matrix-init';
import { size, height, width } from '@vect/matrix-index';

const multiply = (a, b) => {
  const [ ha, wa ] = size(a), [ hb, wb ] = size(b);
  if (wa !== hb) { throw new Error('incompatible sizes') }
  const mx = draft(ha, wb);
  for (let i = 0; i < ha; i++) {
    for (let j = 0; j < wb; j++) {
      let sum = 0;
      for (let k = 0; k < wa; k++) sum += a[i][k] * b[k][j];
      mx[i][j] = sum;
    }
  }
  return mx
};

/**
 * Transpose a 2d-array.
 * @param {*[][]} mx
 * @returns {*[][]}
 */
const transpose = (mx) => {
  const h = height(mx), w = width(mx), cols = Array(w);
  for (let j = 0; j < w; j++)
    for (let i = 0, col = cols[j] = Array(h); i < h; i++)
      col[i] = mx[i][j];
  return cols
};

export { multiply, transpose };