Re: Help with slow model translation

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