def mass_2d(self, r, rho0, Rs):
        """
        mass enclosed projected 2d sphere of radius r
        :param r:
        :param rho0:
        :param a:
        :param s:
        :return:
        """

        sigma0 = self.rho2sigma(rho0, Rs)
        return self.mass_2d_lens(r, sigma0, Rs)
mass enclosed projected 2d sphere of radius r
        :param r:
        :param rho0:
        :param a:
        :param s:
        :return: