[Cbc] Getting information from running model in CbcMain1

[acw at ascent.com]

Thank you, Stefan: that works like a charm.

Also, to John Forrest: perhaps I neglected to reply to your last 
suggestion for tracking down a bug in my driver4-like application.  Your 
suggestion enabled me to find my problem, and we're now cooking along 
happily.

This forum is a very useful and supportive place.  Thanks to all of you.



From:
Stefan Vigerske <stefan at math.hu-berlin.de>
To:
acw at ascent.com
Cc:
cbc at list.coin-or.org
Date:
02/19/2009 02:11 PM
Subject:
Re: [Cbc] Getting information from running model in CbcMain1



Hi,

I do this by given a callback function to CbcMain1.
The callback always gets the current model, so you can get, e.g., the
model after preprocessing.

It looks like the following:

CbcModel* preprocessedmodel=NULL; /* global variable */
int gamsCallBack(CbcModel* currentSolver, int whereFrom) {
     if (whereFrom==3) preprocessedmodel=currentSolver;
     return 0;
}

int main (int argc, const char *argv[]) {
 ...
 CbcModel model(lp);
 ...
 CbcMain1(par_list_length,cbc_args,model,gamsCallBack);
 ...
}

See
https://projects.coin-or.org/GAMSlinks/browser/stable/0.4/GAMSlinks/src/Cbc/GamsCoinCbc.cpp

for the full code.

Best,
Stefan

acw at ascent.com wrote:
> We have a Cbc application modeled on Cbc/examples/driver4.cpp; in 
> particular, it uses the function CbcMain1 to actually launch the 
solution.
> 
> In a previous version of the same application, we mimicked something 
much 
> simpler, more like driver1.cpp.  In that version, we were able to 
monitor 
> the problem as it was being solved.  We used calls like 
> CbcModel->getObjValue() in another thread to watch the objective 
> improving.  (We are aware of thread hazards, but we were pretty careful 
to 
> protect ourselves from them.)
> 
> When we switched to the driver4-like approach, this stopped working. 
> CbcMain1 makes its own copy of the given Cbc model, and it is on this 
copy 
> (called "cbcModel" in the code, which is in CbcSolver.cpp) that 
> CbcModel.branchAndBound() is actually invoked.  Poking the original 
model 
> to find out its best objective so far, or the number of nodes it has 
> processed, doesn't work.
> 
> Is there a right way to expose this copied model so that outside code 
can 
> query its progress?  I'm reluctant to mess around with the code in 
> CbcSolver.cpp, but will do that if I have to.
> 
> 
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> 
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-- 
Stefan Vigerske
Humboldt University Berlin, Numerical Mathematics
http://www.math.hu-berlin.de/~stefan

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