Re: Help with slow model translation

[Heinrich Schuchardt]

On 2/21/20 6:26 PM, Heinrich Schuchardt wrote:
> On 2/21/20 5:46 PM, Greg Gruber wrote:
> > Hello,
> >
> > I have a model that I have developed using MathProg, that I am using
> > regularly. Some problem datasets result in very large models. The
> > problem itself is solving very quickly, but I am finding the model
> > translation (reading the .mod file, data files, and setting up the
> > problem) to be very slow.
> >
> > I came across this on the wikipedia entry: " The take-home message is
> > that nested set iterations should be avoided where possible, as these
> > greatly expand the dimensionality and size of the model space to be
> > processed.", and it discusses a case on the OSeMOSYS energy model where
> > the execution time was reduced from 15 hours to 9 minutes by a
> > reformulation.
> >
> > Unfortunately, I'm not sure what they mean here, and I am looking for an
> > example. I have tried searching the OSeMOSYS site for more information,
> > as well as searching for publications by Jonas Horsch, who did the
> > reformulation, but have had no luck yet.
> >
> > Does anybody have examples illustrating how to avoid nested-set
> > iterations in MathProg?
> >
> > Thanks in advance,
> > Greg
> Hello Greg,
>
> please, provide an example model which shall be simplified.
>
> Best regards
>
> Heinrich
> >

Thanks for the example model.

Using the GMPL language is not very efficient to formulate the complex
constraints you have.

For creating the problem formulation for very large problems I would
always prefer using a programming language like Java to generate the
model formulation and directly call the solver library from the
programming language.

Your problem has more than 30 million variables. I doubt that you will
get a solution for this size of a problem with GLPK.

Best regards

Heinrich