code: def to_binary(self,filename):
          
  
          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)
docs: 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