topic Re: reductions by OPTMODEL / OPTLP presolvers in Mathematical Optimization, Discrete-Event Simulation, and OR

reductions by OPTMODEL / OPTLP presolvers

deleted_user — Wed, 22 Sep 2010 15:10:25 GMT

Hi SAS/OR users,
First of all, thanks to SAS developpers for amazing works done for the OPTMODEL procedure. Really impressive!
Just one question, I currently "play" with presolver optmodel to detect constraints eliminated in a LP problem

eg : reset presolver = none; solve; expand / con;

but i didn't see any differences in SAS outputs with
solve; expand / con;

Is there any options to see the constraints removed by OPTMODEL presolver? by OPTLP presolver?

thank you

Re: reductions by OPTMODEL / OPTLP presolvers

Philipp_SAS — Wed, 22 Sep 2010 15:52:28 GMT

Hi,

For the OPTMODEL presolver it is possible to see the model that is actually passed on to the solver by using the SOLVE option in the expand command. The OPTMODEL presolver only does small changes to the model, for many instances none at all.

The OPTLP (or other solvers like OPTMILP etc.) presolver uses very advanced presolving techniques and often ends up with a totally different model. Explaining in the output how this model relates to the original is far to complicated and usually not needed. So it is not possible to access this model from the SAS language.

I hope this answers your question.

Philipp

Re: reductions by OPTMODEL / OPTLP presolvers

deleted_user — Thu, 23 Sep 2010 14:01:48 GMT

Thanks Philipp