code: function scaleRow (M, row, scale) {
    const me = M.elements;
    let i = row;
    let alpha = (scale === undefined ? 1.0 : scale);
    me[i] *= alpha;
    me[i + 3] *= alpha;
    me[i + 6] *= alpha;
  }
docs: Scales the row in the matrix given by the index.
  @memberof Helpers
  @param {Matrix2|Matrix3|Matrix4} M The matrix.
  @param {number} row The row index.
  @param {number} scale The number to scale by.