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

[Matthew Galati]

John,

As far as I can tell, if I do not enableSimplexInterface before 
getBasics, I fail an assertion because pivotVariable( ) is NULL. I tried 
turning the special option on just before it, but this did not help.

Matt

> 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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>                                        Mustafa Rasim Kilinc                
>                                        <mrk304 at lehigh.edu>, Jeff Linderoth 
>              05/17/06 05:39 PM         <jtl3 at lehigh.edu>                   
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>              Please respond to                                     Subject 
>              Discussions about         Re: [Coin-discuss] OSI, CLP pivot   
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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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