Page 1 of 1

### relational operators within GAMS

Posted: Tue Aug 01, 2017 9:36 am
Hi all,
Please tell me, can we use relational operators within loop in GAMS. Please refer following code:

loop(k,
loop(i,
loop(t,
a.l(k,i,t)=l=b(i);
);
);
);
where k,i,t are sets while a (k,i,t) is variable and b(i) is parameter.

Thanks
Garvis Garg

### Re: relational operators within GAMS

Posted: Tue Aug 01, 2017 2:47 pm
Hi, you can't define "lower else" equations with loops

if you want to initialize the variable "a" without relationship between the sets, use the next code: a.l(k,i,t) = b(i);

For use relational operators within loop in GAMS you have to define the relationship with "\$" statement, for example:

suppose the next relationships:
k greater or equal than 1
i greater or equal than k
t lower than i+1

using loop and "\$":
loop(k\$(ord(k) ge 1),
loop(i\$(ord(i) ge ord(k),
loop(t\$(ord(t) lt ord(i)+1),
a.l(k,i,t)=b(i);
);
);
);

you can use subset too:
In this example, sets k and i does not have restriction, but set t depend on k and i following the "selection" subset

loop((k,i),
loop(t\$selection(t,k,i),
a.l(k,i,t)=b(i);
););

best regard

### Re: relational operators within GAMS

Posted: Thu Aug 03, 2017 8:19 am
no in my problem I am using

eq(i)..sum((k,t),a.l(k,i,t))=l=b(i);

tell me the use of relational operator within the loop is possible or not.
If not possible then please tell me any alternate way to solve this problem.

Thanks
Garvis Garg

### Re: relational operators within GAMS

Posted: Thu Aug 03, 2017 8:58 pm
For your case you must use "\$"

Suppose the next relationships:
i greater or equal than 1
k lower or equal than i
t greater or equal than k

eq(i)\$(ord(i) ge 1).. sum((k,t)\$(ord(k) le ord(i) and ord(t) ge ord(k)), a(k,i,t)) =l= b(i);

You do not need use the "loop" command

Best regard

### Re: relational operators within GAMS

Posted: Thu Jul 12, 2018 12:06 pm
Dear,

I have a problem with loop statement.

set P /P01 * P08/
Jn /Jn01 * Jn10/
Jm /Jm01 * Jm10/
parameters p1(P,Jm)
p2(P,Jn);

I would like to have the following: p1(P,jm) = p2(P,jn) - the values jn from p2 to be taken to jm in p1, for each P.

I tried this:
for(P,
for (jm
(p1(P,jm) = p2(P,jn));
);
);

My problem here is to change the dimension only and to keep all the values of the parameter the same.

### Re: relational operators within GAMS

Posted: Sat Jul 14, 2018 11:17 am
You could use a mapping

Code: Select all

``````set P /P01 * P08/
Jn /Jn01 * Jn10/
Jm /Jm01 * Jm10/
mapN_M(Jn,Jm) /#Jn:#Jm/;

display mapN_M;

parameters p1(P,Jm)
p2(P,Jn);

p2(P,Jn) = uniform(0,10);

loop((jn,jm)\$mapN_M(jn,jm),
p1(P,jm) = p2(P,jn);
);
display p1, p2;

For information on the mapping, see [url]https://www.gams.com/latest/docs/UG_SetDefinition.html[/url].

Cheers
Renger

``````

### Re: relational operators within GAMS

Posted: Mon Jul 16, 2018 8:47 am
Thank you, it works !!