calculate log(metropolis ratio times hastings factor)

def _get_log_rho_metropolis_hastings(self, proposed_point, proposed_eval):
        """calculate log(metropolis ratio times hastings factor)"""
        return self._get_log_rho_metropolis(proposed_point, proposed_eval)\
             - self.proposal.evaluate      (proposed_point, self.current) \
             + self.proposal.evaluate      (self.current, proposed_point)