想生成如下的一对序列,把x2的cita设为0,但是为什么总是只生成一个数据,后面的全是NA
workfile random2 u 1 2500
series e1=@nrnd
series e2=@nrnd
e1(1)=0
e2(1)=0
series x1
series x2
x1(1)=0.1
x2(1)=0.5
series u1
series u2
u1(1)=0
u2(1)=0
series h1
series h2
h1(1)=1
h2(1)=1
smpl 2 2500
h1=0.05+0.9*h1(-1)+0.05*u1(-1)*u1(-1)
u1=@sqrt(h1)*e1
x1=0.1+0.1*x1(-1)+u1
h2=0.1+0.85*h2(-1)+0.1*u2(-1)*u2(-1)
u2=@sqrt(h2)*e2
x2=0.5+0.05*x2+u2