data 5_2;
t=intnx('month','31jan2012'd,_n_-1);
format t yymm7.;
input qcxl@@;
cards;
1.3356  1.4969  1.6117  1.7702  1.9442  2.1661
2.2455  2.5876  2.8304  3.1904  3.5168  3.7401
4.1221  4.5082  5.0853  5.4052  6.0638  6.6251
7.0048  7.9586  8.9926  9.6036  10.5498 11.7885
;
run;
proc nlin data=5_2 method=gauss;
model qcxl=a*b**t;
parameters a=1.2 b=1.1;
der.a=b**t;
der.b=a*t*b**(t-1);
output out=result p=p;
run;
这条程序是拟合一条指数型的曲线，不知道什么地方出错了，输出的结果是这样的：

                                                  The NLIN Procedure

Execution Errors for OBS 1:
NOTE: Missing values were generated as a result of performing an operation on missing values.       Each place is
      given by (number of times) AT (statement)/(line):(column).


                                       1 AT 1/273:15 1 AT 2/275:8 1 AT 3/276:12
Execution Errors for OBS 2:
NOTE: Missing values were generated as a result of performing an operation on missing values.       Each place is
      given by (number of times) AT (statement)/(line):(column).


                                       1 AT 1/273:15 1 AT 2/275:8 1 AT 3/276:12
Execution Errors for OBS 3:
NOTE: Missing values were generated as a result of performing an operation on missing values.       Each place is
      given by (number of times) AT (statement)/(line):(column).

我不太懂，求教各位啦！