two shock in two time in a loop

GAMS
1

hello my friends

I work in a recursive dynamic CGE model.
my set is
t time /1*20 /;
I want to have one shock from t=1 to t=4 (for example increase tax) and I want to have another shock from t=5 to t=20 (for example increase productivity). But I do not know how I can write a loop for this purpose. please help me

2

Hi

You can loop over the whole horizon and change the parameters for the shocks. Here some example code:

set t Periods /1*20/;

set sc /BAU, SHOCK/;

parameter parshock(sc,t)  Shock some parameters

parshock(sc,t) = 0;
parshock("SHOCK",t)$(t.val < 5) = 2;
parshock("SHOCK",t)$(t.val > 4) = 3;

loop(sc,
   loop(t, 
      myparam = parshcok(sc,t);
      solve model...
      change capital using investments
      );
 );

I usually add for each scenario a set like the following:

set sc /BAU, SHOCK/,
     BAU(sc)  /BAU/,
     SHOCK(sc)  /SHOCK/;

Now I can run the loop for a specific scenario without having to run all the other scenarios.

loop(sc$(shock(sc),
    ....

Cheers
Renger

3

Thank you very much

4

I did exactly that, but when I increase the time, for example, from 20 to 30 years, my answer is different.
For example for t /120/
I increase the tax rate (t.val<5) then the average GDP decrease 0.5 % from the first year to fifth year
when t is /130/
and I increase the tax rate (t.val<5) then the average GDP decrease by 0.8 % from the first year to the fifth year.
I think it is wrong.