def X2_chain_H0_omgega_m(self, args):
        """
        routine to compute X^2
        :param args:
        :return:
        """
        #extract parameters
        [H0, omega_m] = args
        Ode0 = self._omega_lambda_fixed
        logL_H0, bool_H0 = self.prior_H0(H0)
        logL_omega_m, bool_omega_m = self.prior_omega_m(omega_m)
        logL = logL_H0 + logL_omega_m
        if bool_H0 is True and bool_omega_m is True:
            logL += self.LCDM_lensLikelihood(H0, omega_m, Ode0)
        return logL + logL_H0 + logL_omega_m, None