code: function isRowNonzero (M, i, TOL = 1e-14) {
    const me = M.elements;
    return !(Compare.isZero(me[i], TOL) &&
              Compare.isZero(me[i + 3], TOL) &&
              Compare.isZero(me[i + 6], TOL));
  }
docs: Tests if a row in a matrix is nonzero.
  @memberof Helpers
  @param {Matrix2|Matrix3|Matrix4} M The matrix.
  @param {number} i The row index.
  @param {number} TOL The numerical tolerance.