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