[Cbc] Clues sought on how to diagnose Cbc performance changes

Wed Dec 17 12:54:19 EST 2008

My previous reply did not seem to show up...

Allan,

If you look at driver4.cpp in Cbc/examples then that should give you the
speed of the stand-alone version in your application.

John Forrest

  From:       acw at ascent.com                                                                                             

  To:         cbc at list.coin-or.org                                                                                       

  Date:       12/16/2008 07:15 PM                                                                                        

  Subject:    [Cbc] Clues sought on how to diagnose Cbc performance changes                                              

A little while ago I sent the following message to Coin-discuss.  The last
time I paid serious attention, there was no mailing list devoted to Cbc,
but now I discover that there is, and this was probably a better place to
ask my question.  I apologize to those who are seeing my query twice.
----- Forwarded by Allan C Wechsler/Cambridge/Ascent on 12/16/2008 07:11 PM
-----

 From:    acw at ascent.com                                                   

 To:      coin-discuss at list.coin-or.org                                    

 Date:    12/16/2008 06:14 PM                                              

 Subject: [Coin-discuss] Clues sought on how to diagnose Cbc performance   
          changes                                                          

About two years ago, we built an application around the then-current
release of Cbc.  For the sake of discussion, call this "Version A."

Very recently, we downloaded a much more recent release, and re-architected
the application.  This "Version B" has exactly the same API as Version A,
but the details of the systems integration are different in a variety of
ways.

Version A was essentially a hack-job on CbcMain's command-line interface:
for example, it launched the Cbc solver by faking a "branch" command.
Version B, in contrast, was written along the lines of some of the simpler
examples in Cbc/examples, and since it leaves out most of the machinery of
the command-line interface, it's about a factor of ten shorter.

To my (perhaps naive) surprise, Version B is far less efficient than
Version A.  On one small example problem, Version A processed 24 nodes to
solve the problem, while Version B processed 52 nodes, more than twice as
many.

It is obvious that we have made at least one ill-advised change in cut,
node, or branch selection, or in presolve/postsolve processing.  We have
avoided customizations we did not understand, and in most cases used the
default choices that were implicit in the two versions of Cbc.

We have tried more-or-less blind flailing in our attempts to regain the
lost performance efficiency, exploring Version A and experimenting with
transplanting various customizations from there to Version B, but nothing
has had an effect of more than about 10%, compared to the more than 2-to-1
discrepancy between the two versions.

Obviously Cbc has not regressed; it is our own ignorance of how to
configure it that is at fault.  But we don't even know how to begin the
analysis that would reveal fruitful avenues to take.  We would appreciate
any advice.  I haven't provided much detail about our configuration,
because I don't know what aspects of it are important, but I'd be pleased
to answer any questions that would help someone give us some guidance.

Thank you for your consideration, and for the enormous amount of work that
has clearly been put into making Cbc a useful tool.
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