code: function addB(product, left, right) {
    for (var i = 0; i < product.deltas.length; i++) {
      left.deltas[i] = product.deltas[i];
      right.deltas[i] = product.deltas[i];
    }
  }
docs: adds {from} deltas to {left} and {right} deltas
  @param {Matrix} product
  @param {Matrix} left
  @param {Matrix} right