[Coin-discuss] Inconsistency between Osi Solves

[Ashutosh Mahajan]

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
>      > _______________________________________________
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> 
>      --
>      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

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--
regards
Ashutosh Mahajan
http://www.lehigh.edu/~asm4

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