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Re: [Help-glpk] fixing the value of a variable
From: |
Andrew Makhorin |
Subject: |
Re: [Help-glpk] fixing the value of a variable |
Date: |
Sat, 6 Jan 2007 10:24:16 +0300 |
> I have a linear program which works fine with variables and fixed
> parameters. But I want to fix values of some variables for testing
> purposes.
> More specifically, I have a set of variables and constraints in my
> model file:
> set x;
> var vars{x};
> subject to constraint1{i in x}:
> vars[i] ... ;
> And data file defines the members of the set.
> set x := x1 x2;
> This works fine, but I want to assign a constant to vars[x1] and see the
> output of the program and its effect on the other variables. I cannot
> put constraints in my model file using names x1 or x2 because they are
> not defined yet, and I cannot define the value of vars[x1] in data file
> because set x is formed of variables. Does anyone know a way of doing
> this without changing variables to parameters?
The following way is not elegant, but it must work in glpsol 4.13:
var vars{j in x}, >= if ... then -Infinity else c[j],
<= if ... then +Infinity else c[j];