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Re: [Help-glpk] Working with larger numbers

From: Michael Hennebry
Subject: Re: [Help-glpk] Working with larger numbers
Date: Tue, 29 Jul 2008 21:47:00 -0500 (CDT)

On Tue, 29 Jul 2008, Markus Pilz wrote:

> Andrew Makhorin wrote:
> > I think that Markus obtains a solution, where some flows are
> > non-integral while he expects them to be integral due to network
> > structure and integral arc capacities (I mean max flow and min cost flow
> > problems). On the other hand, it is unclear to me why this could happen,
> > because the constraint matrix is an indicent matrix of the network, so
> > the basis matrix being an incident matrix of the spanning tree is
> > triangular and therefore its LU-factorization is trivial and should be
> > exact even in floating-point arithmetic. I suspect that there are some
> > additional constraints in the model.
> >
> Yes, I expect the mentioned integral solutions as arc capacities are
> integral.
> The min cost flow is described as minimum cost circulation. Does this
> formulation contain the "additional constraints" you mention?

I think it doesn't.
If all you have are flow conservation equations and flow limits,
integer data should give you an integer solution,
even with floating point arthmetic.

Michael   address@hidden
"Those parts of the system that you can hit with a hammer (not advised)
are called Hardware;  those program instructions that you can only
curse at are called Software."

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