> library(forecast)
> fit<-auto.arima(gdp)#自动求出最优的p,d,q
> fgdp$model
Series: gdp
ARIMA(2,2,2)
Coefficients:
ar1 ar2 ma1 ma2
-0.1858 0.3515 -0.4327 -0.5295
s.e. 0.2424 0.0933 0.2512 0.2425
sigma^2 estimatedas 3273: log likelihood=-1400.25
AIC=2810.49 AICc=2810.73 BIC=2828.22
从R中的auto.arima()函数估计的gdp模型为:
gdp(t)=-0.1858gdp(t-1)+0.3515gdp(t-2)+e(t)-0.4327e(t-1)-0.5295e(t-2)
模型这样写对不对?
I(2)体现在哪里?