def is_cptp(self, atol=None, rtol=None):
        """Return True if completely-positive trace-preserving."""
        if self._data[1] is not None:
            return False
        if atol is None:
            atol = self._atol
        if rtol is None:
            rtol = self._rtol
        accum = 0j
        for op in self._data[0]:
            accum += np.dot(np.transpose(np.conj(op)), op)
        return is_identity_matrix(accum, rtol=rtol, atol=atol)