说明：   GCV Generalized cross-validation.广义交叉校验,用做非线性时间序列的计算，非常有用，找了好久才找到的。不要错过机会哦
(GCV Generalized cross-validation. Generalized cross-validation, using nonlinear time series to do the calculation, is very useful to find for a long time to find the. Oh, do not miss the opportunity to)