[Symphony] Unexpected behaviour of gap_limit in symphony 5.1

[Pierre.Lebodic at lri.fr]

> We have now made a new release 5.1.11 that fixes this bug if you want
> to continue to use 5.1.
I will continue working with 5.1 until 5.2 becomes faster for the
instances I'm working on. Thanks a lot for this fix as well as for the
whole work done on SYMPHONY.

Pierre

> It's actually still present in 5.2, though it
> didn't exhibit itself on the example you sent. We fixed it in the
> stable branch of 5.2, but have not made a new release yet.
>
> Cheers,
>
> Ted
>
> On Sat, Sep 12, 2009 at 9:31 AM,  <Pierre.Lebodic at lri.fr> wrote:
>> Hello,
>>
>> I mentioned earlier a "bug" involving gap_limit in SYMPHONY 5.1.10. It
>> should be possible to reproduce it with the following test instance:
>> http://www.lri.fr/~lebodicp/wp-content/uploads/gap_instance.MPS
>>
>> In the following, cuts are disabled to prevent possible numerical
>> surprises.
>> In SYMPHONY 5.1.10, with gap_limit set to 5 (for instance), the
>> following
>> happens:
>> ****************************************************
>> * Optimal Solution Found                           *
>> * Now displaying stats and best solution found...  *
>> ****************************************************
>> ...
>> Current Upper Bound:         2.304
>> Current Lower Bound:         1.300
>> Gap Percentage:              43.58
>>
>> Solution Found: Node 0, Level 0
>> Solution Cost: 2.304
>>
>> and a feasible solution is displayed. Although the gap percentage is
>> 43.58, the solver indicates that the optimal has been found.
>>
>> In SYMPHONY 5.1.10, with gap_limit set to -1, a better solution is
>> provided:
>> ****************************************************
>> * Optimal Solution Found                           *
>> * Now displaying stats and best solution found...  *
>> ****************************************************
>> ...
>> Solution Found: Node 5, Level 3
>> Solution Cost: 2.062
>>
>> and the optimal solution is displayed.
>>
>>
>> SYMPHONY 5.2 seems to work: with gap_limit lower than 43.58, the optimal
>> solution is found. with gap_limit set higher than 43.58, it provides the
>> same feasible solution as SYMPHONY 5.1.10.
>> Thanks for your help.
>>
>> Cheers,
>>
>> Pierre
>>
>> _______________________________________________
>> Symphony mailing list
>> Symphony at list.coin-or.org
>> http://list.coin-or.org/mailman/listinfo/symphony
>>
>
>
>
> --
> Dr. Ted Ralphs
> Associate Professor, Lehigh University
> (610) 628-1280
> ted 'at' lehigh 'dot' edu
> coral.ie.lehigh.edu/~ted
>