[Cbc] Another problem "long to be solved"

[John Forrest]

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

On 17/11/14 11:43, Yves Touchard wrote:
> Hello,
>
> I split an huge problem in several little problems which sizes are 
> (IMO) equivalent.
> Solving each of them lasts several seconds (no more than 2-3 seconds) 
> except one (several minutes).
> I tried different combination of options (w/wo diving, w/wo zero 
> root...) without any success. (threads 104 ratio 0.05 cutlength 40 
> multiple 4 divingv on divingl on divingf on divingg on divingc on 
> divingp on zero root)
>
> Have you an idea to help this problem to be fastly solved ? Or my 
> splitting and the cost function are not well balanced ?
> The constraint file may be downloaded here:
> https://www.dropbox.com/s/lbd7o2bdn5392m1/long.lp?dl=0
> One of the sol file may be downloaded here:
> https://www.dropbox.com/s/a7foc860ap6lbmn/long.txt?dl=0
>
> I use the the trunk version, revision #2092, compiled with gcc 4.9.0
>
> Thanks and regards
>
> Yves
>
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