这是我从王群勇上照搬的蒙特卡洛模拟程序，怎么不出结果，问题在哪里？谢谢

program rdwalk5,rclass
version 10
syntax [,n(integer 1000)
drop _all
quietly set obs 'n'
capture drop y x1 x2 x3 x4 x5 rndy rndx1 rndx2 rndx3 rndx4 rndx5
quietly {
    gen rndy=100+(1000-100)*invnorm(uniform())
    gen rndx1=10+(100-10)*invnorm(uniform())
    gen rndx2=9+(22-9)*invnorm(uniform())
    gen rndx3=2+(12-2)*invnorm(uniform())
    gen rndx4=6+(24-6)*invnorm(uniform())
    gen rndx5=0+(100-0)*invnorm(uniform())
    gen y=rndy
    gen x1=rndx1
    gen x2=rndx2
    gen x3=rndx3
    gen x4=rndx4
    gen x5=rndx5
    replace y=y[_n-1]+rndy[-n] in 2/'n'
    replace x1=x1[_n-1]+rndx1[-n] in 2/'n'
    replace x3=x3[_n-1]+rndx2[-n] in 2/'n'
    replace x4=x4[_n-1]+rndx3[-n] in 2/'n'
    replace x5=x5[_n-1]+rndx4[-n] in 2/'n'
    regress y x1 x2 x3 x4 x5
    matrix matb=e(b)
    matrix matv=e(V)
    return scalar b=el(matb,1,2)
    return scalar se=sqrt(el(matv,2,2))
  }
end
simulate beta=(r(b)) se=(r(se)),reps(10000) nodots:rdwalk