docs: def _compute_smooth_during_construction(self, xi):
          """
          Evaluate value of smooth at x-value xi.
  
          Parameters
          ----------
          xi : float
              Value of x where smooth value is desired
  
          Returns
          -------
          smooth_here : float
              Value of smooth s(xi)
          """
          if self._variance_in_window:
              beta = self._covariance_in_window / self._variance_in_window
              alpha = self._mean_y_in_window - beta * self._mean_x_in_window
              value_of_smooth_here = beta * (xi) + alpha
          else:
              value_of_smooth_here = 0.0
          return value_of_smooth_here