[Coin-discuss] Controlling printing for CbcStrategyDefault

[John J Forrest]

Viva Italia.

Kish,

The difference in time for aflow3a is because the preprocessing default was
to find SOS.  It did so and on this problem this was not a good idea.

So far I can not reproduce the Clp error messages.  It may not be an error
as such but maybe an infeasible branch (so with bad bounds) slipped through
to solver which threw it out.  Normally these messages would be off.  I
will try a bit more.

John Forrest


                                                                           
             Kish Shen                                                     
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             07/09/06 02:17 AM         Re: [Coin-discuss] Controlling      
                                       printing for CbcStrategyDefault     
                                                                           
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Hi,

On Saturday 08 July 2006 07:31, Kish Shen wrote:

> One question about this preprocessing: do you expect it to improve the
> performance? In my case, I have already called CglPreprocess on the
problem
> when it was first copied from the OsiClpSolver to the CbcModel, and in
the
> rather limited test examples I have been running (mainly used to test if
my
> changes are working, rather than for measuring performances), where some
> MIPLIB problems are solved (but they are modelled in our ECLiPSe
> programming language, rather than read in from an MPS file), doing this
> second preprocessing in CbcStrategy does not improve the solving times,
and
> in fact for one problem (noswot), it slows the solving time time from 33s
> to 54s.
>

I decided to try out some more tests with my code. With the
CbcStrategyDefault
set for the CbcModel  (model is a CbcModel*):

   (code taken and modified from sample2.cpp in Cbc Samples directory)
    // Set up pre-processing to find sos if wanted
    if (lpd->presolve) strategy.setupPreProcessing(2);
    //strategy.setupPrinting(*model, 0);
    model->setStrategy(strategy);
    model->branchAndBound();

this generally solved the problems faster than if the strategy
preprocessing
and setStrategy code is commented out. However, for a couple of the
problems
I tried (versions of MIPLIB's cap6000 and aflow30a), I got what looks like
error messages from Clp:

Clp6002E 1 bad bound pairs or bad objectives were found - first at C3013
Clp6002E 1 bad bound pairs or bad objectives were found - first at C1987
Clp6002E 1 bad bound pairs or bad objectives were found - first at C3863

the actual objective value for the MIP problem after the search appears to
be
correct though. Is the above a potential problem, or are such messages
expected?

aflow30a, in addition to generating Clp error messages like the above, also

ran much slower with the CbcStrategyDefault than without -- slowing down
from
2000 seconds to 6500 seconds, the only problem to do so. Is this related to

the above messages?

Cheers,

Kish Shen
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