def summary(self):
        """Return a formatted string giving a quick summary
        of the results."""

        res = ("nlive: {:d}\n"
               "niter: {:d}\n"
               "ncall: {:d}\n"
               "eff(%): {:6.3f}\n"
               "logz: {:6.3f} +/- {:6.3f}"
               .format(self.nlive, self.niter, sum(self.ncall),
                       self.eff, self.logz[-1], self.logzerr[-1]))

        print('Summary\n=======\n'+res)
Return a formatted string giving a quick summary
        of the results.