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Re: [Help-glpk] initial basis

From: Michael Hennebry
Subject: Re: [Help-glpk] initial basis
Date: Thu, 17 Sep 2009 08:53:31 -0500 (CDT)
User-agent: Alpine 1.00 (DEB 882 2007-12-20)

On Wed, 16 Sep 2009, Andrew Makhorin wrote:

I create a problem, then optimize it, and save status for variables and
constraints, and delete the problem.
I create a new problem, early the same as the first one : I only remove
some variables (and so modify/remove some constraints).
Is there a way, in this configuration, to use the statuses of the first
optimization ? The number of basis variable in the first optimization is
not the same as the number of rows in the second, but the basis of the
first optimization could be usefull  for the second.

If the number of basic variables is not equal to the number of rows,
the basis is invalid and therefore cannot be used as initial basis
(at least glpk does not provide such a feature).

Rather than removing basic variables, that invalidates the basis, you
could fix them at zero; this gives the same effect, however, keeps the
basis valid.

If only using the statuses,
one could also try to remove the entries for the absent variables.
Getting the numbering right might be tricky.

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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