dear dynare, I want to know the following command’s means, and what is it?

```
stoch_simul(order=1,irf=20,nomoments) y ce ch re rh abh ;
ex_=[ 0.001169*ones(12,1); zeros(16,1)];
y0=oo_.dr.ys;
dr=oo_.dr;
iorder=1;
y_=simult_(y0,dr,ex_,iorder);
```

Thanks a lot.