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Re: [Help-glpk] Identical variables

From: Andrew Makhorin
Subject: Re: [Help-glpk] Identical variables
Date: Sat, 20 Dec 2008 01:11:23 +0300

> Just as a note I also have variables that are anti-symmetric, i.e., x =
> -y, but I assume that these will be covered as well.

In the glpk distribution there is an example model, jssp.mod (the
job-shop scheduling problem). Binary variables Y[i,j,a] in that model
are used to represent a precedence relation, namely, Y[i,j,a] = 1
means job i is scheduled before job j on machine a, and 0 means job j
is scheduled before job i, thus, Y[i,j,a] = 1 - Y[j,i,a] due to
asymmetry. I experimented with a version of the model, where the half
of Y variables were eliminated, and surprisingly the solution time was
a bit greater than for the original model (may be this is explained
by some specific properties of the model).

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