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Re: [Help-glpk] Constraint Problem

From: Andrew Makhorin
Subject: Re: [Help-glpk] Constraint Problem
Date: Sun, 26 Aug 2007 13:18:26 +0400

>    I need your help.when I write the constraint section of '.mod'
> file in GNU MathProg,I met a question.My problem is like this : 
>   set I;
>   set J;
>   set K;

>  param interval,>0;
>   param cap{i in I},integer>0;
>   param efc{j in J,k in K}>0;
>   var yesno{i in I,j in J,k in K},binary; 
>   var pnum{i in I,j in J,k in K},integer,>=0;
>   s.t.xz2{i in I,j in J}:(sum{k in
> K}yesno[i,j,k]-1)*interval<=cap[i]*nl-sum {k in
> K}(efc[j,k]*pnum[i,j,k]);

>     because I found that when sum{k in K} yesno[i,j,k] is not
> more than 1, I will get the wrong answer,I decide change this
> constraint to:
>   s.t.xz2{i in I,j in J}:if sum{k in K}yesno[i,j,k]<=1 then 0
> else (sum{k in K}yesno[i,j,k]-1)*interval<=cap[i]*nl-sum {k in
> K}(efc[j,k]*pnum[i,j,k]); 
>     then the glpsol said"operand preceding<= has valid type","modal
> processing error".
>    Can you help me solve this problem ?Thank you!

yesno[] is a variable, not a parameter, so you cannot use it in a
condition, because this leads to a non-linear constraint not allowed
in glpk. You need to reformulate that constraint.

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