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

[acw at ascent.com]

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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