code: def fitted(self, fid=0):
          
          self._checkid(fid)
          return not (self._fitids[fid]["fit"] > 0
                      or self._fitids[fid]["fit"] < -0.001)
docs: Test if enough Levenberg-Marquardt loops have been done.
  
          It returns True if no improvement possible.
  
          :param fid: the id of the sub-fitter (numerical)