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Re: [Help-glpk] Objective value returns even though dual infeasibility i

From: Michael Hennebry
Subject: Re: [Help-glpk] Objective value returns even though dual infeasibility is reported
Date: Thu, 20 Aug 2009 15:36:37 -0500 (CDT)
User-agent: Alpine 1.00 (DEB 882 2007-12-20)

On Thu, 20 Aug 2009, Sam Seaver wrote:

I'm using Flux Variability Analysis to understand how a metabolic
network may change under different conditions.  I'm using glpk, and
for all of the reactions, I am able to get an objective value.  For
some of the reactions, glpk reports that the primal solution is
unbounded because the dual solution is infeasible.  However, the very
same program still prints out an objective value, and not necessarily
zero, or infinity.  Furthermore, the objective value is reasonable.

Reasonable, but not optimal.

Firstly, I do not understand how LP can calculate an objective value
if it can prove that the primal solution is unbounded.  Secondly, I
would like to know, since the metabolic network is a published
standard, how I can tackle the dual infeasibilities without making any
changes to the network.  Is it possible to use the objective values
despite the dual infeasibilities, and whether I can or cannot, what
should I say to an audience of bioengineers about these dual

If the numbers represent something physical,
unbounded is probably wrong.
Your model probably needs fixing.

Michael   address@hidden
"Pessimist: The glass is half empty.
Optimist:   The glass is half full.
Engineer:   The glass is twice as big as it needs to be."

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