Hello to all
I have a scheduling problem that I want to solve with CPLEX…
The model works fine with a small amount of jobs. However when
increasing this amount, Cplex begins to give approximate values for my
binary variables (near 1 or near 0) which causes a conflict of two
jobs working simultaneously on the same machine. Of course, I know
this is an NP-hard problem, but I want to know if there is a way for
avoiding such a problem.
Thank you.
Jose
\
Check up whether you actually declared those variables as binary variables. Maybe that will help
From: José Miguel Quesada
To: gamsworld
Sent: Tuesday, February 14, 2012 8:39 PM
Subject: Cplex roundig problem
Hello to all
I have a scheduling problem that I want to solve with CPLEX…
The model works fine with a small amount of jobs. However when
increasing this amount, Cplex begins to give approximate values for my
binary variables (near 1 or near 0) which causes a conflict of two
jobs working simultaneously on the same machine. Of course, I know
this is an NP-hard problem, but I want to know if there is a way for
avoiding such a problem.
Thank you.
Jose
–
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They are binary, that’s not the problem…
Thanks anyway
Jose
From: gamsworld@googlegroups.com [mailto:gamsworld@googlegroups.com] On Behalf Of stephen kabantiok
Sent: martes, 14 de febrero de 2012 02:34 p.m.
To: gamsworld@googlegroups.com
Subject: Re: Cplex roundig problem
Check up whether you actually declared those variables as binary variables. Maybe that will help
From: José Miguel Quesada
To: gamsworld
Sent: Tuesday, February 14, 2012 8:39 PM
Subject: Cplex roundig problem
Hello to all
I have a scheduling problem that I want to solve with CPLEX…
The model works fine with a small amount of jobs. However when
increasing this amount, Cplex begins to give approximate values for my
binary variables (near 1 or near 0) which causes a conflict of two
jobs working simultaneously on the same machine. Of course, I know
this is an NP-hard problem, but I want to know if there is a way for
avoiding such a problem.
Thank you.
Jose
–
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Dear Arne
Thank You very much.
You were right, a have been working with Big M formulations. I had tested before by increasing the value of the Big M and the problem became unfeasible…I hadn’t tested though by reducing this value. I did it today and the rounding problem was solved, as you said, faster, and also the optimal value was better…I really appreciate your help for I had this problem since November…
Best Regards
MS. José Miguel Quesada Pérez
Departamento de IngenierÃa Industrial
Tecnológico de Monterrey, Campus Querétaro
52 (442) 238 3100 Ext: 6349
Fax: (442) 238 32 70
Enlace intercampus: 8 0 776 6349
Correogptwtec
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From: gamsworld@googlegroups.com [mailto:gamsworld@googlegroups.com] On Behalf Of Arne Stolbjerg Drud
Sent: miércoles, 15 de febrero de 2012 10:02 a.m.
To: gamsworld@googlegroups.com
Subject: SV: Cplex roundig problem
Jose:
If you get conflicts with rounded binary variables then it suggests that you have some very large coefficients in your model. I think you should look after big-M formulations and reduce your coefficients as must as possible. This process will also often reduce the solution time.
Good luck
Arne Stolbjerg Drud
\
Arne Stolbjerg Drud
ARKI Consulting & Development A/S
Bagsvaerdvej 246A, DK-2880 Bagsvaerd, Denmark
Phone: (+45) 44 49 03 23, Fax: (+45) 44 49 03 33, email: adrud@arki.dk
Fra: gamsworld@googlegroups.com [mailto:gamsworld@googlegroups.com] På vegne af José Miguel Quesada Pérez
Sendt: 15. februar 2012 16:08
Til: gamsworld@googlegroups.com
Emne: RE: Cplex roundig problem
They are binary, that’s not the problem…
Thanks anyway
Jose
From: gamsworld@googlegroups.com [mailto:gamsworld@googlegroups.com] On Behalf Of stephen kabantiok
Sent: martes, 14 de febrero de 2012 02:34 p.m.
To: gamsworld@googlegroups.com
Subject: Re: Cplex roundig problem
Check up whether you actually declared those variables as binary variables. Maybe that will help
From: José Miguel Quesada
To: gamsworld
Sent: Tuesday, February 14, 2012 8:39 PM
Subject: Cplex roundig problem
Hello to all
I have a scheduling problem that I want to solve with CPLEX…
The model works fine with a small amount of jobs. However when
increasing this amount, Cplex begins to give approximate values for my
binary variables (near 1 or near 0) which causes a conflict of two
jobs working simultaneously on the same machine. Of course, I know
this is an NP-hard problem, but I want to know if there is a way for
avoiding such a problem.
Thank you.
Jose
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