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Re: [Help-glpk] Fixed values in Variable statement

From: Andrew Makhorin
Subject: Re: [Help-glpk] Fixed values in Variable statement
Date: Wed, 2 Jul 2008 22:48:11 +0400

> I'm trying to specify fixed values to some variables in an array using =
> expression (see "4.3 Variable statement" in GMPL Reference). Something
> like this:
>     set MySet;
>     set MySubset within MySet;
>     var X {i in MySet} = if i in MySubset then 0 else binary;

> or, similarly:
>     var X {i in MySet diff MySubset}, binary;
>     var X {i in MySubset} = 0;

> How can i do this in GMPL?

*All* elemental variables in the array of variables can be fixed as

var x{...} = <numeric expression> ;

However, to fix *some* elemental variables you should use correspodning
equality constraints, for example:

s.t. fpp{i in MySubset}: x[i] = 0;

This is normal, because such constraints will be removed by the mip

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