feasible model identified as infeasible

GAMS
1

Hi everybody

I´m solving a Mixed integer nonlinear programming model using AlphaECP. There is a instance wich i know is feasible, but after running GAMS said that it is feasible.
I set this parameters:
option MINLP=alphaecp,NLP=snopt,DOMLIM=10000,Iterlim=10000, reslim=604800;

Does anyone know what could be the problem?

Thank you so much

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2

Hi,

Is your model pseudo-convex?

GAMS/AlphaECP is a global solver for pseudo-convex (a slightly more general class than convex) MINLP problems , otherwise it works as a local solver. Hence, no guarantee of finding a feasible solution to a non-pseudoconvex MINLP problem can be given. However, in practice GAMS/AlphaECP has been able to find a good solution for several non-pseudoconvex models, especially, if the model has none or very few non-linear equality constraints. In order to increase the chances of finding a solution to a model you can try to reduce the number of cutting planes generated by each iteration by setting GAMS/AlphaECP option CUTnrcuts to, for example, 0.05. Hence, you can try to add the following code before the solve statement and modify the modelname to correspond to your model name.

$onecho > alphaecp.opt
CUTnrcuts 0.05
$offecho
modelname.optfile=1;

Best,
Toni

On Tuesday, July 9, 2013 9:00:02 PM UTC+2, hdez....@gmail.com wrote:

Hi everybody

I´m solving a Mixed integer nonlinear programming model using AlphaECP. There is a instance wich i know is feasible, but after running GAMS said that it is feasible.
I set this parameters:
option MINLP=alphaecp,NLP=snopt,DOMLIM=10000,Iterlim=10000, reslim=604800;

Does anyone know what could be the problem?

Thank you so much

–
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