def METHOD_NAME(self, M, z):
    """Computes the radius R_200 crit of a halo of mass M in physical mass M/h.
    :param M: halo mass in M_sun/h
    :type M: float or numpy array
    :param z: redshift
    :type z: float
    :return: radius R_200 in physical Mpc/h
    """
    return (3 * M / (4 * np.pi * self.rhoc_z(z) * 200)) ** (1.0 / 3.0)