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Re: [Help-glpk] type of variables

From: Nigel Galloway
Subject: Re: [Help-glpk] type of variables
Date: Tue, 06 Sep 2011 04:48:44 -0700

That is a good start.
GLPK can use this as a biasis for integer optimisation. The output from simplex is a solution based on a continuous number system. You want a discreet solution. It would be nice if just rounding the continuous solution to the nearest integer produced the answer. Usually it doesn't.
You must next call glp_intopt  using your simplex produced basis as the parameter.
To obtain the answer you must then use glp_mip_col_val for individual columns, or glp_print_mip for the entire solution. You might like to also call glp_print_sol and compare how close the actual values in glp_print_mip are to the values in glp_print_sol if you just rounded them. 
Nigel Galloway
On Sep 5 ’11, "name name" <address@hidden> wrote:
I solve it with

  glp_simplex(lp, parm)  routine

On Mon, Sep 5, 2011 at 2:54 PM, Nigel Galloway <address@hidden> wrote:
The question is how do you solve the problem, and how do you obtain the solution.
When you make all these columns binary you have a Diophantine Equation. GLPK can solve these, though there are other ways which may be better.
GLPK will first solve it as a linear problem. It is then necessary to perform Integer Optimization.
Having done this there are different routines to obtain the integer optimal solution as opposed to the linear solution.
Nigel Galloway
On Mon, 05 Sep 2011 14:26 +0200, "name name" <address@hidden> wrote:

On Mon, Sep 5, 2011 at 1:18 PM, Nigel Galloway <address@hidden> wrote:
Do you obtain this value with GLPK.glp_get_mip_col_val ?

no with .glp_set_col_kind
Even if the type of variable is binary Lp give non integer value
Nigel Galloway
On Mon, 05 Sep 2011 09:52 +0200, "name name" <address@hidden> wrote:

I have a very strange problem

I solve un Lp problem but the and the value of my  variables are not ineger I got x(0,1)=0.2... even thaught when I print the type of my variables I got 3 coresponding to type binary( I got type to binary for all variables with GLPK.glp_set_col_kind(lp, i, GLPKConstants.GLP_BV)).

Can you tell my where the problem could be?

Thank you

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