def dump_pmean(self, filename):
        """ Dump parameter means (``fit.pmean``) into file ``filename``.

        ``fit.dump_pmean(filename)`` saves the means of the best-fit
        parameter values (``fit.pmean``) from a ``nonlinear_fit`` called
        ``fit``. These values are recovered using
        ``p0 = nonlinear_fit.load_parameters(filename)``
        where ``p0``'s layout is the same as ``fit.pmean``. The saved
        values can be used to initialize a later fit (``nonlinear_fit``
        parameter ``p0``).
        """
        warnings.warn(
            "nonlinear_fit.dump_pmean deprecated; use pickle.dump instead",
            DeprecationWarning,
            )
        with open(filename, "wb") as f:
            if self.p0.shape is not None:
                pickle.dump(numpy.array(self.pmean), f)
            else:
                pickle.dump(collections.OrderedDict(self.pmean), f)