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Re: [Help-glpk] [Fwd: Re: Is it possible to feed glpsol with a feasible

From: João Flávio de Freitas Almeida
Subject: Re: [Help-glpk] [Fwd: Re: Is it possible to feed glpsol with a feasible initial solution to a MIP problem?]
Date: Sun, 4 Aug 2019 14:26:44 -0300

Dear Alejandro,

1 - Call glpsol to generate a solution of the LP problem and save it using "-w file.sol"
2 - The file.sol file must have a solution line (first) named "s" "bas", ie a basic solution
3 - Call glpsol by disabling LP (--nopresol) and MILP preprocessing (--nointopt) and include the base file (--ini file.sol)

$ glpsol -m localiz.mod -d localiz.dat --nopresol --nomip -w file.sol
$ glpsol -m localiz.mod -d localiz.dat --nopresol --nointopt --cuts --ini file.sol

Andrew, for MIP problems I had the same problem: a file.sol with "mip" solution, but Glpk display an error message:

"error: wrong solution designator; 'bas' expected"

João Flávio de Freitas Almeida
Professor Adjunto
Departamento de Engenharia de Produção
Universidade Federal de Minas Gerais
30.310-290 Belo Horizonte MG Brasil

Em sáb, 7 de abr de 2018 às 11:07, Alejandro Pascual <address@hidden> escreveu:
Hello Chris,

Thank you very much for your concern.

I tried the --nopresol --nointopt options following your suggestion,
but I got the following error message (I attach the log file):

localiz0.sol:8: error: wrong solution designator; 'bas' expected
Unable to read initial basis

Best regards,

On 7 April 2018 at 10:12, Chris Matrakidis <address@hidden> wrote:
> Hi Alejandro,
>> Anyway, I can't get glpsol to use the feasible solutition fed with
>> --ini.
> I think you need to disable the presolver with options --nopresol --nointopt
> to use a given solution. The presolver generates a new problem, for which
> the given solution is no longer valid.
> Best Regards,
> Chris Matrakidis
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