Re: [Help-glpk] problem with simple MIP

[glpk xypron]

Hello Florian,

your problem is not trivial. Without an upper limit on the variables
there is infinite number of solutions with allowable solution values
ranging from 0 to infinity.

The following solves well:
var x_1, integer, >=0, <= 10;
var x_2, integer, >=0, <= 10;
var x_3, integer, >=0, <= 10;
var x_4, integer, >=0, <= 10;
s.t. c1 : 1 <= 2*x_1 + 3*x_2 - 2*x_3 - 3*x_4;
solve;
end;

---

The current version of GLPK is 4.47.

GLPK 4.43 is available in Ubuntu 10.10 (Maverick), and
Ubuntu 11.10 (Oneiric).

Best regards

Xypron

-------- Original-Nachricht --------
> Datum: Tue, 01 Nov 2011 13:59:03 +0000
> Betreff: [Help-glpk] problem with simple MIP

> Hello,
> 
> I tried to use glpk to get a solution for the following almost trivial
> MIP "feasibility" problem
> 
> 1 <= 2*x_1 + 3*x_2 - 2*x_3 - 3*x_4 (x_i non-negative integers)
> 
> but the solver didn't finish within 15h. Changing the coefficient of x_4
> from -3 to -1, -2, -4, or -5 gives (correct) solutions immediately. I'm
> a bit puzzled now. It would be great if anyone could enlighten me?
> 
> See below for more information. I'm happy to provide more details if
> needed.
> 
> Thanks,
> Florian

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