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conditional-statementsgams-math
rkza
rkza

Reputation: 53

How to add a condition to a variable - GAMS

In the model I'm trying to build, I have a variable defined as:

Variables
    x(i,j)  number of motors produced in month i to be delivered in month j ;

In that variable, j must always be equal or greater than i for it to make sense (you can't produce something in this month to be delivered in the previous month). However, I have no clue as to how I can properly model this. I've searched and couldn't find an easy solution to this.

Any ideas?

Upvotes: 3

Views: 360

Answers (2)

Lutz
Lutz

Reputation: 2292

You should use "variables with limited domains" for this, look here for more details, it is a rather new GAMS feature: https://www.gams.com/latest/docs/UG_ModelSolve.html#UG_ModelSolve_LimitedDomain

So, in your example, it would look like this:

Set limX(i,j) limiting domain of x;

limX(i,j) = ord(j) >= ord(i);

Model m /all, x(limX)/;
...

Edit: Corrected syntax of model statement.

Upvotes: 2

Raquel Aguiar
Raquel Aguiar

Reputation: 73

So, I add this, right after declaring the variable: 

x.fx(i,j)$(ord(i)>ord(j))=0;

It is fixing the values of the variables you are not using to zero. In your model:

enter image description here

And the results are:

enter image description here

I believe that should do it :)

Upvotes: 1

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