各位好:我想用SAS产生时间序列的数据,我有个时间序列模型,X(t)=0.2X(t-1)+0.1X(t-3)+0.2X(t-5)+0.3X(t-10)+0.1X(t-15)+Z(t),
想根据这个模型产生序列长度为1000的观测,不知如何产生,请高手帮忙!
非常感谢!
DATA AR;
ARRAY OBS OBS1-OBS50; *** Room is made for 50 observations;
OBS (1) = RANNOR (-1); *** The most recent observation in the series;
DO J = 2 TO 50;
OBS (J) = SQRT(.70) * OBS (J-1) + SQRT(.30) * RANNOR(-1);
END; OUTPUT;
KEEP OBS1-OBS50;
PROC TRANSPOSE OUT=AR1; *** The series is transposed into a column for PROC ARIMA;
DATA AR1; SET AR1;
PROC ARIMA DATA = AR1; IDENTIFY VAR=COL1 NLAG=1; *** The AR1 lag value is estimated;
ESTIMATE P = 1;
RUN;
上面的程序是我在SAS For Monte carlo study 这本书中找到的,书中提到的SQRT必须相加为1,这里我就有些搞不懂为何相加为1,而且这个sqtr是何种东东呢?正常情况下不就是系数吗?系数为何相加为1呢?而我的模型是个疏系数模型,并非是他所谓的常见的模型,这里怎么产生我所述的时间序列模型呢?
请高手帮忙,谢谢大家!