[Symphony] help with interpreting the output (does symphony continue after finding optimal solution?)

Tue Jun 29 04:16:30 EDT 2010

mps file  :-). run it on cplex just to find out :-)
nice to produce new instances that hurt...and well done to symphony (!)
Claude ph Medard

On Tue, Jun 29, 2010 at 12:20 AM, Ted Ralphs <ted at lehigh.edu> wrote:

> Just to follow up, I ran SYMPHONY with more detailed output and
> everything looked fine for me---it terminated right after finding the
> first feasible solution. Are you still seeing this behavior? If you
> want, you can solve the instance with verbosity set to "3" and send me
> the output so I can see what's happening. By the way, I also tried
> solving this instance with the latest version of Cbc and after a few
> days and over 1000 nodes, it still hasn't found  feasible solution.
> I'm not sure why it's having so much trouble.
>
> In any case, this seems to be an interesting instance for testing. Are
> you willing to say more about the origin of this instance and/or
> provide more of the same? I would encourage you to consider submitting
> it for inclusion in MIPLIB 2010:
>
> http://miplib.zib.de/miplib2010/
>
> Doing so will ensure that solver developers are aware of the
> difficulties of solving this class of instances and may target the
> development of solver capabilities for better handling this kind of
> structure.
>
> Cheers,
>
> Ted
>
> On Thu, Jun 24, 2010 at 10:54 AM, Ted Ralphs <ted at lehigh.edu> wrote:
> > I ran the instance myself on the trunk version of SYMPHONY and it
> > solves in only 15 nodes, but it ook almost a day on a reasonably fast
> > machine. So the biggest reason why it's taking so long is that the LP
> > relaxations appear to be very difficult to solve. You could possibly
> > cut down the running time by parallelizing, but given that the tree is
> > so small, this might not buy you much. I'm doing another run now with
> > more detailed output to see exactly what's going on with the bounds.
> >
> > Ted
> >
> > On Thu, Jun 17, 2010 at 6:32 AM, Ted Ralphs <ted at lehigh.edu> wrote:
> >> The output is rounded to two digits of precision. My guess is that
> >> even though it appears that the bounds are equal, they differ in less
> >> significant digits. You could try setting "gap_limit" to something
> >> like .01 and see if it finishes more quickly. Can you send me the
> >> model off-line?
> >>
> >> Cheers,
> >>
> >> Ted
> >>
> >> On Sun, Jun 13, 2010 at 7:10 PM, Iulian Ober <iulian.ober at irit.fr>
> wrote:
> >>> Hello,
> >>>
> >>> I'm trying to use Symphony (5.2.4) off-the-shelf (no custom code) to
> solve a large ILP problem (a 0/1 problem actually).
> >>> For this problem I know that all feasible solutions have value = 81,
> like the LP optimal solution.
> >>> The output seems to indicate that the solver continues to search long
> after finding an optimal solution, but maybe I'm misinterpreting it. Here is
> a condensed version of what I get:
> >>>
> >>> =================================================
> >>> Starting Preprocessing...
> >>> Preprocessing finished...
> >>>         coefficients modified: 47022
> >>>         constraints removed: 7116
> >>>         variables fixed: 1844
> >>> Problem has
> >>>         33846 constraints
> >>>         8560 variables
> >>>         403100 nonzero coefficients
> >>>
> >>> Total Presolve Time: 0.689973...
> >>>
> >>> Solving...
> >>>
> >>> solving root lp relaxation
> >>> done: 0 left: 1 ub: ?? lb: ?? time: 20
> >>> done: 0 left: 1 ub: ?? lb: ?? time: 40
> >>> ...
> >>> ...
> >>> done: 0 left: 1 ub: ?? lb: ?? time: 1524
> >>> The LP value is: 81.000 [0,54820]
> -- found the continuous solution ?
> >>> ...
> >>> ...
> >>> done: 0 left: 1 ub: ?? lb: ?? time: 10979
> >>> done: 1 left: 2 ub: ?? lb: 81.00 time: 10999                    -- does
> this mean it found a feasible integer solution for 81 ?
> >>> ...
> >>> ...
> >>> done: 6 left: 7 ub: ?? lb: 81.00 time: 14783
> >>> done: 17 left: 12 ub: 81.00 lb: 81.00 gap: 0.00 time: 22276     -- is
> this because no direction for the optimization is specified in the MPS
> model, so it tries both?
> >>> ...
> >>> ...
> >>> done: 28 left: 1 ub: 81.00 lb: 81.00 gap: 0.00 time: 74648
> >>>
> >>> ****************************************************
> >>> * Optimal Solution Found                           *
> >>> * Now displaying stats and best solution found...  *
> >>> ****************************************************
> >>> ...
> >>> ...
> >>> =======================================================
> >>>
> >>> Can anybody please help me interpret the output ?
> >>> I tried to augment verbosity (verbosity 3), but then I get fewer output
> (!?) -- no periodic messages every 20 sec anymore...
> >>>
> >>> I also tried to set :
> >>>        find_first_feasible 1
> >>> but does not seem to finish quicker, so maybe I'm wrong...
> >>>
> >>> Thanks for your help,
> >>>
> >>> Iulian Ober
> >>> IRIT, Universite de Toulouse
> >>> 118 route de Narbonne
> >>> 31062 Toulouse, France
> >>> http://www.irit.fr/~Iulian.Ober/ <http://www.irit.fr/%7EIulian.Ober/>
> >>>
> >>>
> >>> _______________________________________________
> >>> 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 <http://coral.ie.lehigh.edu/%7Eted>
> >>
> >
> >
> >
> > --
> > Dr. Ted Ralphs
> > Associate Professor, Lehigh University
> > (610) 628-1280
> > ted 'at' lehigh 'dot' edu
> > coral.ie.lehigh.edu/~ted <http://coral.ie.lehigh.edu/%7Eted>
> >
>
>
>
> --
> Dr. Ted Ralphs
> Associate Professor, Lehigh University
> (610) 628-1280
> ted 'at' lehigh 'dot' edu
> coral.ie.lehigh.edu/~ted <http://coral.ie.lehigh.edu/%7Eted>
>
>
> _______________________________________________
> Symphony mailing list
> Symphony at list.coin-or.org
> http://list.coin-or.org/mailman/listinfo/symphony
>
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