def X2_chain_H0(self, args):
        """
        routine to compute X2 given variable parameters for a MCMC/PSO chain
        """
        #extract parameters
        H0 = args[0]
        omega_m = self.omega_m_fixed
        Ode0 = self._omega_lambda_fixed
        logL, bool = self.prior_H0(H0)
        if bool is True:
            logL += self.LCDM_lensLikelihood(H0, omega_m, Ode0)
        return logL, None