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Re: [Help-glpk] Working with larger numbers

From: Markus Pilz
Subject: Re: [Help-glpk] Working with larger numbers
Date: Tue, 29 Jul 2008 10:14:46 +0200
User-agent: Thunderbird (X11/20080724)

Gabor Retvari wrote:
> On Monday 28 July 2008, Markus Pilz wrote:
>> we are working on a tool that utilizes glpk to solve a set of maximum
>> and minimum cost flows. So far, our approach looks promising. (This
>> implies a big thank-you to glpk team.)
>> Currently, we have some difficulties with larger decision variables. For
>> example, if  the variables of a maximisation problem (max flow) are
>> limited by values above 1e9, the solution tends to be inexact.
>> We still can use the solution as a basis for further processing but
>> maybe we lack some lp (or glpk) basics to obtain exact values in a wider
>> range.
> Wouldn't it be plausible to run GLPK over precise arithmetics? You can do 
> this by calling lpx_exact instead of lpx_simplex. 
> Network flow problems tend 
> to be seriously overconstrained and thus highly degenerate, calling for 
> numerical instability. An exact solver would solve this issue, for the prize 
> of being somewhat slower. I mean, *really* slower.

Yes you are right. We already moved to lpx_exact, but it does not help

Best regards

> Best regards, 
> Gabor
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