code: def functional(self, fnct, x, y, sd=None, wt=1.0, mxit=50, fid=0):
          
          self._fit(fitfunc="functional", fnct=fnct, x=x, y=y, sd=sd, wt=wt,
                    mxit=mxit, fid=fid)
docs: Make a non-linear least squares solution.
  
          This will make a non-linear least squares solution for the points
          through the ordinates at the abscissa values, using the specified
          `fnct`. Details can be found in the :meth:`linear` description.
  
          :param fnct: the functional to fit
          :param x: the abscissa values
          :param y: the ordinate values
          :param sd: standard deviation of equations (one or more values used
                     cyclically)
          :param wt: an optional alternate for `sd`
          :param mxit: the maximum number of iterations
          :param fid: the id of the sub-fitter (numerical)