[Coin-discuss] Inconsistency between Osi Solves

[Pedro Teixeira]

thank you, Ashutosh!
at least, I know it's really my bug now :)

[]'s
Pedro

On Feb 7, 2008 11:18 PM, Ashutosh Mahajan <asm4 at lehigh.edu> wrote:

> pedro,
>  the optimal solution to the mps file posted seems to be 10. i tried with
> cplex, xpress, symphony, cbc and even clp (branch and bound).
> some valid constraints may be missing from your model.
>
> ashutosh
>
> On Thu, 07 Feb 2008, Pedro Teixeira wrote:
>
> >    The situation is as follows (I'm running the latest stable of all
> >    projects, should I be running from the trunk?)  :
> >
> >    Both Cbc and Sym give the same straight objetive value of 10.  Where
> for
> >    this instance the known optimal is 85. The strange thing is that with
> Clp,
> >    the first result is 110 but then I add an extra cut (subtour) and it
> >    becomes infeasible...
> >
> >    It's really probably something in my code, but it seems Clp was
> closer to
> >    what I wanted.. I posted the issue here because I was surprised to
> get
> >    different solutions. I'm also trying to run in cplex, but as you
> suggested
> >    I'll stick with Cbc and Sym, disregard Clp and will review the code
> again
> >    :/
> >
> >    Ashutosh, I copied the model here:
> >    [1]http://www.pedro.not.br/tmp/model.mps
> >
> >    thanks for the replies.
> >    Pedro
> >
> >    On Feb 7, 2008 1:20 PM, Ted Ralphs <[2]ted at lehigh.edu> wrote:
> >
> >      As far as I remember, the branchAndBound() method of Clp is a
> fairly
> >      basic implementation that is not really intended for practical use.
> You
> >      probably want to compare with OsiCbc for solving integer programs.
> It
> >      should give better results.
> >
> >      Cheers,
> >
> >      Ted
> >      Pedro Teixeira wrote:
> >      > Hi,
> >      >
> >      > I am new to coin-or and not sure if this is the appropriate list
> to
> >      > post. I'm getting very different solutions when using the same
> model
> >      > but switching from OsiClpSolverInterface and
> OsiSymSolverInterface.
> >      >
> >      > my current usage is simple:
> >      >
> >      > si->loadFromCoinModel(model , true);
> >      > si->initialSolve();
> >      > si->branchAndBound();
> >      >
> >      > With ClpSolver, it takes much more time and I get (for
> illustration):
> >      > Search took 43600 iterations and 7302 nodes
> >      > Clp0000I Optimal - objective value 115
> >      >
> >      > However, with SymSolver I get the result instantaneously:
> >      > Solution Found: Node 1, Level 1
> >      > Solution Cost: 10.000
> >      >
> >      > Shouldn't I get the same results? Or is there any known issues
> with
> >      Osi?
> >      > Can anyone shed in any light?
> >      >
> >      > cheers,
> >      > Pedro
> >      > _______________________________________________
> >      > Coin-discuss mailing list
> >      > [3]Coin-discuss at list.coin-or.org
> >      > [4]http://list.coin-or.org/mailman/listinfo/coin-discuss
> >
> >      --
> >      Dr. Ted Ralphs
> >      Associate Professor
> >      Industrial and Systems Engineering
> >      Lehigh University
> >      (610)758-4784
> >      ted at lehigh dot edu
> >      [5]coral.ie.lehigh.edu/~ted
> >
> > References
> >
> >    Visible links
> >    1. http://www.pedro.not.br/tmp/model.mps
> >    2. mailto:ted at lehigh.edu
> >    3. mailto:Coin-discuss at list.coin-or.org
> >    4. http://list.coin-or.org/mailman/listinfo/coin-discuss
> >    5. http://coral.ie.lehigh.edu/%7Eted
>
> > _______________________________________________
> > Coin-discuss mailing list
> > Coin-discuss at list.coin-or.org
> > http://list.coin-or.org/mailman/listinfo/coin-discuss
>
>
> --
> regards
> Ashutosh Mahajan
> http://www.lehigh.edu/~asm4 <http://www.lehigh.edu/%7Easm4>
>
>
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