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

[Michael Hennebry]

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
> infeasibilities?

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."