code: def residuals(self, pars, x, y, order):
          
  
          return y - self.fourier_series(pars, x, order)
docs: Residual of Fourier Series.
  
          Parameters
          ----------
          pars : array_like
              Fourier series parameters.
          x : array_like
              An array of date.
          y : array_like
              An array of true values to fit.
          order : int
              An order of Fourier Series.