write the parameter ensemble to a jco-style binary file

        Parameters
        ----------
        filename : str
            the filename to write

        Returns
        -------
        None


        Note
        ----
        this function back-transforms inplace with respect to
        log10 before writing

def to_binary(self,filename):
        """write the parameter ensemble to a jco-style binary file

        Parameters
        ----------
        filename : str
            the filename to write

        Returns
        -------
        None


        Note
        ----
        this function back-transforms inplace with respect to
        log10 before writing

        """

        retrans = False
        if self.istransformed:
            self._back_transform(inplace=True)
            retrans = True
        if self.isnull().values.any():
            warnings.warn("NaN in par ensemble",PyemuWarning)
        self.as_pyemu_matrix().to_coo(filename)
        if retrans:
            self._transform(inplace=True)