[Coin-discuss] Suggestions on how to go about tuning?

[Rolf Steenge]

John,
You wrote :
 
"Again looking at log I saw that Cbc could work out that valid objective
values had to be a multiple of 0.1 so any solution has to be 0.1 better
than previous.  Going back to original formulation and setting that
value of 0.1 gave  31K nodes but 305 seconds"
 
How do you set that value of 0.1? Or have you added a constraint such as
sum of cijxij - 10 xn = 0 with xn a new integer variable.
 
Best regards
Rolf
 

-----Original Message-----
From: coin-discuss-bounces at list.coin-or.org
[mailto:coin-discuss-bounces at list.coin-or.org] On Behalf Of John J
Forrest
Sent: Saturday, June 03, 2006 16:02
To: Discussions about open source software for Operations Research
Subject: Re: [Coin-discuss] Suggestions on how to go about tuning?



Philip, 

I said I would play about with your problem and report on what I did and
how I went about it : 

All these experiments were with stand alone solver - SOS is a bit
trickier and I will get to that later.  Also symmetry breaking would
help but I would need help in CglPreProcess and/or pointers to relevant
papers. 

The first thing to do is solve the problem however slowly and look at
log and solution.  Using defaults this took 1148 seconds and 150K nodes.
Looking at the log file it looked as if strong branching was not buying
very much.  What was more interesting was that all variables took
integer values although only half were declared integer.  Assuming this
would always be true I tried setting them all integer.  This time strong
branching was kicking in and it took 5K nodes and 413 seconds.  I also
saw that cuts and heuristics were not doing much good so switched them
off.   

Again looking at log I saw that Cbc could work out that valid objective
values had to be a multiple of 0.1 so any solution has to be 0.1 better
than previous.  Going back to original formulation and setting that
value of 0.1 gave  31K nodes but 305 seconds.  Finally in this phase of
tuning I tried switching off strong branching as my hunch was that it
might cost too much for the effect gave an increase in nodes to 38K but
the time dropped to 233 seconds. 

Further ideas such as just having some (but not the original set)
variables integer gave various perturbations on time and nodes but no
significant improvement. 

I have started looking at SOS possibilities but am not far along.   

Basically I use multiple runs and an editor and grep to try and get a
feel for problem. 

John Forrest

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