[Cbc] Another problem "long to be solved"

[Yves Touchard]

John,

Sorry for the delay of this reply.

With the divesolves option the 'long problem' is not so long...! It is still longer than other equivalent problems but it's reasonable.
Furthermore, all my NRTs are done with this option without loss of performance.

But, i have some questions for you:

  *   Using the divesolves option automatticaly enables the other dive options?
  *   And, why using both divesolves and divingvectorlength extends the solving time (x2) ?
  *   How can i finely choose the value of the divesolves option?

Regards

Yves

John Forrest john.forrest at fastercoin.com <mailto:cbc%40list.coin-or.org?Subject=Re:%20Re%3A%20%5BCbc%5D%20Another%20problem%20%22long%20to%20be%20solved%22&In-Reply-To=%3C546B3584.9070306%40fastercoin.com%3E>
Tue Nov 18 07:03:16 EST 2014

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________________________________

Yves,

In trunk there are some new/modified options.

There was a parameter "experiment".  I have left some old meanings, but
introduced some new ones.  For difficult problems I would suggest
-experiment 3000 !!.  This actually switches on multiple root solvers
(4), does more aggressive preprocessing, adds some extra root cut
generators AND switches on most diving heuristics.

When I tried, the code had no problems with long.lp, but I would suggest
you look at a new parameter divesolves.  This can increase the number of
solves a diving heuristic can do.  The bottom digit is ignored for
number of solves but can switch on something which could help you a
lot.  Normally the diving heuristics fix some integer variables if they
are at their bound, however they do not fix satisfied general integer
variables - not at bound - so if 0 <= x <= 20 and x is at 12 then it
does not get fixed.  I have allowed this behaviour to change so
-divesolves 301 will allow up to 300 solves and will fix some satisfied
general integers.

You may also want to look at diveoptions and even set -DDIVE_PRINT=1 in
configure.  This switches on some printout which may help you understand
what is happening in which heuristic.

John


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