def as_xyzt_string(self):
        """
        Returns a string of the form 'x, y, z, +1', '-x, -y, z, -1',
        '-y+1/2, x+1/2, z+1/2, +1', etc. Only works for integer rotation matrices
        """
        xyzt_string = SymmOp.as_xyz_string(self)
        return xyzt_string + ", {:+}".format(self.time_reversal)