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Re: [Help-glpk] problem with simple MIP
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From: |
Andrew Makhorin |
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Subject: |
Re: [Help-glpk] problem with simple MIP |
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Date: |
Wed, 09 Nov 2011 03:34:52 +0300 |
> I tried to use glpk to get a solution for the following almost trivial
> MIP "feasibility" problem
>
> 1 <= 2*x_1 + 3*x_2 - 2*x_3 - 3*x_4 (x_i non-negative integers)
>
> but the solver didn't finish within 15h. Changing the coefficient of x_4
> from -3 to -1, -2, -4, or -5 gives (correct) solutions immediately. I'm
> a bit puzzled now. It would be great if anyone could enlighten me?
>
This happens because of unbounded integer variables. Using Gomory cuts
(--gomory) may help.