[Scip] scaling

[Mahr Tamas]

Thank you for looking into this!

I wonder if the problem is really at soplex. I have tried to solve the  
same problem with the soplex shell command, and it can solve it very  
quickly. (I guess it solves the lp relaxation of the mip, but I am  
guessing here. In fact I have no clue how soplex interprets a mip.)

Looking into the soplex code reveals that their cli program uses the  
MySoPlex class that is derived from the SoPlex class. The scip  
interface class for soplex (SPxSCIP), however, is derived from a  
different line, namely the SPxSolver class. This class is a sibling of  
the SoPlex class. Unfortunately, the SPxSolver class do not use the  
presolver or scaler classes that are used in the SoPlex class. That is  
why the command line program can solve this problem, while the scip  
solver cannot.

I think either the SPxSCIP class should be derived from the SoPlex  
class and then it could make use of the scaling/presolving classes in  
there, or the SPxSCIP class could at least mimic the SoPlex class by  
applying the presolving/scaling classes in a similat manner. But maybe  
I am totally wrong here, and scaling/presolving should happen already  
in scip at the beginning of the branch-and-bound search and not in  
soplex every time an lp relaxation is solved.

Tamas

On 2008.11.26., at 18:55, Tobias Achterberg wrote:

>
>
> Hans D. Mittelmann wrote:
>> I ran it with SCIP/CPLEX (also possible for free through
>> neos.mcs.anl.gov) and it solves it. So does SCIP/CLP.
>
> Thanks! This seems to indicate that the Soplex guys should take a  
> closer look. I will forward Tamas' mail to them.
>
>
> Tobias