def _forecast_error(self, steps):
        sigma2 = self.sigma2
        ma_rep = arma2ma(np.r_[1, -self.arparams],
                         np.r_[1, self.maparams], nobs=steps)

        fcerr = np.sqrt(np.cumsum(cumsum_n(ma_rep, self.k_diff)**2)-sigma2)
        return fcerr
dataset/ETHPy150Open statsmodels/statsmodels/statsmodels/tsa/arima_model.py/ARIMAResults._forecast_error/operator `*` -> `-`