Dear Jacques,

I did the following in order to understand how GAMS handles this structure that you ask.

set t /1*10/;

parameter P(t), R(t),d;

P(t)=uniform(0,1);

R(t)=P(t)-P(t-1);

d=R(‘1’);

display d, R, P;

From the results you can see that R(1)=P(1) because there is no 0 label (e.g. P(0)).

Hope that helped,

Konstantinos Petridis

Î¤Î· Î ÎÎ¼Ï€Ï„Î·, 12 Î”ÎµÎºÎµÎ¼Î²ÏÎ¯Î¿Ï… 2013 1:02:05 Î¼.Î¼. UTC+2, Î¿ Ï‡ÏÎ®ÏƒÏ„Î·Ï‚ Jacques ÎÎ³ÏÎ±ÏˆÎµ:

Thank you Constantinos,

This works, but I would like to be sure that it is necessary, in order to optimize the code.

What would be the value of R(t)=P(t)-P(t-1) for t=1, if I do not define P(‘1’) specifically ?

P(t-1) is “out of range”, so how does GAMS handle it ?

Thx,

Jacques

Le jeudi 12 dÃ©cembre 2013 11:49:06 UTC+1, ÎšÏ‰Î½ÏƒÏ„Î±Î½Ï„Î¯Î½Î¿Ï‚ Î ÎµÏ„ÏÎ¯Î´Î·Ï‚ a Ã©crit :

Hello Jacques,

I think you should try the following:

*Here you ensure that R(‘1’)=0

EQ1(t)$(ORD(t)=1)… R(t)=e=0;

*Here you compute R(t) for t>1

EQ2(t)$(ORD(t) gt 1)… R(t)=P(t)-P(t-1);

Hope that helps,

Konstantinos Petridis

Î¤Î· Î ÎÎ¼Ï€Ï„Î·, 12 Î”ÎµÎºÎµÎ¼Î²ÏÎ¯Î¿Ï… 2013 12:40:10 Î¼.Î¼. UTC+2, Î¿ Ï‡ÏÎ®ÏƒÏ„Î·Ï‚ Jacques ÎÎ³ÏÎ±ÏˆÎµ:

Hello everyone !

I want to substract two consecutive values of a parameter and I am worried about the sets…

Here is my problem :

P(t) is defined over t from 1 to 10

Then I define R(t)=P(t)-P(t-1)

What is the value of R(‘1’) ? Can I be sure that it is P(‘1’) ?

ideally I would like to have R(‘1’)=0…

Thx for your help !

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