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[Help-glpk] glpsol.exe differs from AMPL

From: Michael Bramley
Subject: [Help-glpk] glpsol.exe differs from AMPL
Date: Wed, 27 Jun 2012 17:10:47 -0400



I am running glpk MIP and in AMPL and finding that the order of the solutions differ.  For example, say I have a model where I need to maximize an objective based upon paired values X, Y, and Z (and each pairing has a score).  I am not using any additional options for the solutions, eg specifying branch&cut, etc.


AMPL will tell me that the solution is X, Y, Z

glpk will tell me the solution is Z, X, Y.


I note that the sum of the scores for each solution is equivalent (as it should be as addition is commutative).


The problem I am trying to reconcile is is there a physical difference between ordering objects X, then Y, then Z with the order of Z, then X, then Y?


Not sure if this is clear to everyone, but the main point is I see differences.


Michael Bramley
tel: +1 513 632 0549


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