Hi my name is Daniel, and I’m new using GAMS. I had to learn the

program because I’m developing a model for synthetise Heat Exchangers

Networks as a master thesis.

Well, I’m writting in this forum because I’ve a problem with DICOPT.

The model developed is parametrized with a variable called DTmin, and

what I do is make an optimization Loop with a pool of values for this

particular variable. In some cases there is an optimal MINLP solution,

but in other cases DICOPT reports the following sentence: “Too many

infeasible NLP subproblems consider the use of infeasder option”

when I analize the Log file it shows something that I think is a clue,

but I can’t understand.

when DICOPT is running shows:

** Feasible Solution. Value of objetive = 45800 (or something like

that), this value is closer to the optimal solution reached for som

values of DTmin.

After this, the program search the solution during 3 iterations (in

phase =3) and then says:

** Loss of feasibility while tightening tolerances - Return to phase

0

the solver iterate once, and find the same old value (45800) and the

problem repeats until MAXCYCICLES gets to the maximum value.

Â¿What can I do for the convergence of my problem?

Â¿Is a good posibility change the infeasder option?, and if is Â¿How can

I do this?

thanks and best regards!!

PS: I’m using as a solvers

CPLEX: LP

CONOPT: NLP

DICOPT: MINLP

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Daniel,

DICOPT calls an NLP and a MIP solver. The log you see is a mixure of

the NLP solver, MIP solver and DICOPT log. The message "** Feasible

Solution. Value of objetive = 45800 " looks like a CONOPT message and

does not give too much info about the solution of your MINLP problem.

You can try to work the INFEASDER option, but you can also try other

MINLP solvers like, AlphaECP, BARON, LindoGlobal, or SBB. I am always

interested in MINLP problems (I manage the MINLPLib at www.gamsworld.eu),

so you can also send a copy of the problem to me (mbussieck@gams.com).

Regards,

Michael Bussieck, GAMSWorld Coordinator

On Jul 21, 1:32 pm, Daniel wrote:

Hi my name is Daniel, and I’m new using GAMS. I had to learn the

program because I’m developing a model for synthetise Heat Exchangers

Networks as a master thesis.

Well, I’m writting in this forum because I’ve a problem with DICOPT.

The model developed is parametrized with a variable called DTmin, and

what I do is make an optimization Loop with a pool of values for this

particular variable. In some cases there is an optimal MINLP solution,

but in other cases DICOPT reports the following sentence: “Too many

infeasible NLP subproblems consider the use of infeasder option”

when I analize the Log file it shows something that I think is a clue,

but I can’t understand.

when DICOPT is running shows:

** Feasible Solution. Value of objetive = 45800 (or something like

that), this value is closer to the optimal solution reached for som

values of DTmin.

After this, the program search the solution during 3 iterations (in

phase =3) and then says:

** Loss of feasibility while tightening tolerances - Return to phase

0

the solver iterate once, and find the same old value (45800) and the

problem repeats until MAXCYCICLES gets to the maximum value.

Â¿What can I do for the convergence of my problem?

Â¿Is a good posibility change the infeasder option?, and if is Â¿How can

I do this?

thanks and best regards!!

PS: I’m using as a solvers

CPLEX: LP

CONOPT: NLP

DICOPT: MINLP

–~–~---------~–~----~------------~-------~–~----~

To post to this group, send email to gamsworld@googlegroups.com

To unsubscribe from this group, send email to gamsworld-unsubscribe@googlegroups.com

For more options, visit this group at http://groups.google.com/group/gamsworld?hl=en

-~----------~----~----~----~------~----~------~–~—

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