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Re: [Help-glpk] Strange Question

From: Michael Hennebry
Subject: Re: [Help-glpk] Strange Question
Date: Wed, 3 Mar 2004 09:45:01 -0600 (CST)

On Tue, 2 Mar 2004, Welson Sun wrote:

> Hi all, I have met a strange question with Glpk, can you help me out?
> I am using Glpk in Cygwin under WindowsXP. Since currently there is no
> Windows makefile for Glpk JNI, I used the precompiled version from
> address@hidden .
> My LP problem is quite simple:
> Minimize C1X1 + C2X2 + ..... + CnXn
> So that
>     Xi - Xj <= Wij ( 1 <= i,j <= n )
> Where all X are integer and all Wij are non-negtive integer.
> The first strange problem is that I can use simplex() method to solve this,
> while I cannot use integer() method to solve this, the later will report:
> GlpkMsg: lpx_integer: optimal solution of LP relaxation required
> I have set the problem to be MIP type, so how can this be possible?

If you RTFM, you will discover that lpx_integer may only follow lpx_simplex.
If, as seems likely, the constraint matrix is totally unimodular,
you only need lpx_simplex anyway.
If you only use lpx_simplex, don't try to fetch an MIP solution.

The other, I can't help you with.

Mike   address@hidden
"Two roads divurged in a woods, and I took the road less travelled by...
and they CANCELLED MY FRIKKIN' SHOW. I totally shoulda took that road
with all those people on it. Damn."                           --  Joss Whedon

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