[Cbc] Cut efficiency in cbcSolve for versions 2.0.0, 2.1.0, 2.2.2 and 2.3.0

[John J Forrest]

Torsten,

Techniques such as probing can be very expensive and default settings have
been changed between versions.  What happens if you try and force more
probing e.g. -probing forceonstrong?  Also it could be a bug of sorts.

If you want, you can send me the problem for me to see if there is a bug
(as long as it is not too large).

John Forrest


                                                                                                   
  From:       "Torsten Fahle" <Torsten.Fahle at inform-ac.com>                                        
                                                                                                   
  To:         <cbc at list.coin-or.org>                                                               
                                                                                                   
  Date:       08/26/2009 11:32 AM                                                                  
                                                                                                   
  Subject:    [Cbc] Cut efficiency in cbcSolve for versions 2.0.0, 2.1.0,	2.2.2	and 2.3.0          
                                                                                                   
  Sent by:    cbc-bounces at list.coin-or.org                                                         
                                                                                                   





Hi,

When testing with older cbcSolver versions we were surprised  to see that
the lower bound in the root node after adding cuts
differs significantly between different cbc releases:

On a test case the root node after cuts had a lower bound of
195.305  (CBC 2.0.0)
221.561  (CBC 2.1.0)
160.296  (CBC 2.2.2 and 2.3.0)

The initial LP bound is 160.236, the optimal solution 246.296.
This means almost no improvement by root cuts in CBC 2.2.2 and 2.3.0. The
initial gap is 53%
In CBC 2.0.0 and 2.1.0 there is a significant improvement, the initial gap
is 26%, and 11%, resp.

It seems that probing is not as efficient in cbcSolve 2.2.2 and 2.3.0 as it
was in cbcSolve 2.0.0 and 2.1.0( after some tuning). Maybe there is a small
bug in probing or some
other setting stops probing from being as effective as in older versions?

All tests were performed using MS Visual Studio 2005 on an Intel QuadCore
CPU using Debug mode.
There are numerical differences between release and debug version in this
setting. I hope the effect
is nevertheless still reproducible.

I've filed a ticket (#78) with more details on the case. Maybe someone can
investigate this case and find

Thanks !

  Torsten

--

Dr. Torsten Fahle
Airport Systems Division
INFORM GmbH, Pascalstr.23, 52076 Aachen, Germany
Tel. (+49) 24 08 - 94 56 24  FAX: -94 56 25
e-mail: Torsten.Fahle at inform-ac.com   http://www.groundstar.de
INFORM Institut fuer Operations Research und Management GmbH
Registered AmtsG Aachen HRB1144 Gfhr.Adrian Weiler



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