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

[Torsten Fahle]

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 
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