版主各位同学好!
我自己编了一个极大似然估计的程序估计仅有一个截距的方程(yi=ci+ui),如下:
new;
library optmum,PGRAPH;
load y[10,1]=data.txt;
T=rows(y);
START=1;
PRMTR_IN={0.0044 1};
PRMTR_IN=PRMTR_IN';
{xout,fout,gout,cout}=optmum(&lik,PRMTR_in);
"likelihood value is ";
fout;
"Estimated parameters are:";
xout';
proc LIK(PRMTR1);
local prmtr,sigma, C, L,FORC, likv, J_ITER,lik;
PRMTR=PRMTR1;
sigma=PRMTR[1,.];
C= PRMTR[2,.];
LIKV=0.0;
J_ITER=1;
do until J_ITER>T;
Forc=y[J_ITER,1]-C;
L=(1/SQRT(2*PI*sigma))*EXP((-0.5*FORC*FORC/sigma));
LIK=LN(L);
LIKV = LIKV+LIK;
J_ITER = J_ITER+1;
endo;
retp(LIKV);
endp;
数据:
1
1.1
1
1.2
0.9
1
1.05
1
1.04
1
但是,最终结果为:
likelihood value is
-339.45805 - 15.70796i
Estimated parameters are:
-48617429108370469000000000000.00000 -1515226650922.38280
为什么参数会如此大呢,从数据可以看出应该是(0.0044 1)附近。
谢谢!