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[Bug-glpk] Re: minimization flag ignored by 'glp_simplex' (GLPK 4.25)

From: Robbie Morrison
Subject: [Bug-glpk] Re: minimization flag ignored by 'glp_simplex' (GLPK 4.25)
Date: Wed, 2 Jul 2008 17:08:02 +0400

Hi Andrew and other API users

An update.

I modified my problem generator to remove an
'aphysical' mistake -- namely transmission lines with
negative losses (which, I suppose, is equivalent to
letting them suck in power from the aether).  This fix
also corrected the minimization flag problem I had
early experienced (and which was reported in my last

But even so, the flag problem still seems strange.
I don't see how the physicality of the problem could
be an issue.

Should anyone wish to investigate this further, I am
willing to write the original model out as a set of
sequential GLPK calls.  But this is quite some work,
so I would need an expression of interest.

with best wishes

> ----------------------------------------------------------------------
> Message: 1
> Date: Wed, 25 Jun 2008 18:50:47 +0400
> From: Robbie Morrison <address@hidden>
> Subject: [Bug-glpk] minimization flag ignored by 'glp_simplex' (GLPK
>       4.25)
> To: address@hidden
> Message-ID: <address@hidden>
> Content-Type: text/plain; charset=us-ascii
> Hello Andrew and other API users
> I am using GLPK 4.25 (because my transition to 4.28 has
> not yet been completed for the reasons outlined in my
> posting on 06-Jun-2008).
> I am currently experiencing a problem getting
> 'minimization' to stick, even though I set this flag
> explicitly with 'glp_set_obj_dir' and 'glp_get_obj_dir'
> returns 'GLP_MIN' before and after the solver call.
> I have some small test LPs (nodal electricity markets
> as it happens), ranging in size from 4x4 to 100x70, and
> the problem only occurs when I invoke 'glp_simplex'.
> If I switch to 'lpx_interior' instead, everything works
> EXACTLY as expected.

[snip - remainder of post]

Robbie Morrison
Technical University of Berlin, Berlin, Germany
University email (redirected) : address@hidden
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