[Coin-lpsolver] Re: [Coin-discuss] OSI, CLP pivot

[John J Forrest]

Matt,

The code you describe makes it look as if you could just do
enableSimplexInterface at beginning and disable at end - why doesn't that
work?  If there are not too many functions which need to go back to normal
way then maybe I could get those working.

Some things will work if a factorization is kept around (
clp->setSpecialOptions(currentvalue|9).  Set that and then see if you can
do clp->getBasics it does not seem to require enableSimplex but does
require factorization info.  I would think that I could get most things to
work with just a saved factorization except the pivotIn which definitely
needs enableSimplexInterface.

John


                                                                           
             Matthew Galati                                                
             <magh at lehigh.edu>                                             
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Hi John. Thanks! This is much better to be able to just get the sparse row.

The other bottleneck in our codes is related to the enable and disable
simplex interface. It's too messy to strip out the codes and give you a
small sample, but I can tell you the sequence of calls that we use which
involve the simplex interface. We did our best to minimize the number of
calls to enable/disable - but it is still too often. If you have a
special option that could allow us to call this less often, that would
be great.

{
    //solve an LP

    //get basis header
    clp->enableSimplexInterface(false);
    clp->getBasics(head);
    clp->disableSimplexInterface();

    //save warm start
      CoinWarmStartBasis * ws =
    dynamic_cast<CoinWarmStartBasis*>(si->getWarmStart());

    for(...){

      //go back to original ws
      clp->setWarmStart(ws);
      clp->resolve()
      ...

      //get basis header
      clp->enableSimplexInterface(false);
      clp->getBasics(head);
      clp->disableSimplexInterface();

      clp->enableSimplexInterface(false);
      while(...){
          osiclp->getBInvARow(row, abar1, sbar1);
          for(...)
            osiclp->getBInvARow(row, abar2, sbar2);
            clp->pivot(in_col, out_col, out_status);
            clp->disableSimplexInterface();
            clp->enableSimplexInterface(false);
          }
       }
       clp->disableSimplexInterface();
       ...
    }
}

Thanks,
Matt


>Matt,
>
>Done - example code at line 1366 of
Osi/test/OsiClpSolverInterfaceTest.cpp.
>
>You get the underlying CoinIndexedVectors so you can just get nonzeros.
>Zeroing out the contents was optional but may be slightly faster.
>
>John
>
>
>
>
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