[Coin-discuss] OSI, CLP pivot

[Matthew Galati]

Hi John,

One thing that would be an immediate speedup for this kind of thing, is 
to have a version of getBInvARow which does not actually do the memcpy. 
Instead, it would be more efficient, if it just returned a pointer to 
CLP's memory where z and slack exist. In profiling our codes, we have 
found that getBInvARow takes a decent amount of our overall CPU, but 80% 
of getBInvARow is the 2 memcpys.

Is this easy to add? Of course, the user has to promise not to mess up 
that memory.

Matt



>Matt,
>
>If you want to keep to an OsiSolverInterface then I probably can't help,
>but if you know you will be using OsiClpSolverInterface then I may be able
>to help.  If you can put together a driver to go through the steps you want
>then I can see how much faster I can make it - either by adding calls using
>the Clp getModelPtr() or more elegantly by adding a new specialOption bit
>to OsiClpSolverInterface.
>
>John
>
>
>                                                                           
>             Matthew Galati                                                
>             <magh at lehigh.edu>                                             
>             Sent by:                                                   To 
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>             ces at list.coin-or.         software for Operations Research    
>             org                       <coin-discuss at list.coin-or.org>,    
>                                       Mustafa Rasim Kilinc                
>                                       <mrk304 at lehigh.edu>                 
>             04/19/06 09:34 AM                                          cc 
>                                                                           
>                                                                   Subject 
>             Please respond to         [Coin-discuss] OSI, CLP pivot       
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>
>
>If someone wants to do the following, using the "simplex interface":
>{
>  while{
>     //some stuff...
>     ...
>     si->resolve();
>     si->pivot(colIn, colOut, outStatus);
>     ...
>     si->getBasisStatus();
>     si->getBInvARow( );
>     ...
>     //some stuff...
>  }
>}
>
>Is it neccessary to call enable/disableSimplexInterface at every call?
>
>I noticed, that if you pivot, the "basis_" is not updated until
>disableSimplexInterface is called. So, the next call to getBasisStatus
>does not have updated status.
>
>The following seems to work, but is very slow. There is alot of time
>spent in enable/disable.
>
>{
>  while{
>     //some stuff...
>     ...
>     si->resolve();
>     si->enableSimplexInterface();
>     si->pivot(colIn, colOut, outStatus);
>     si->disableSimplexInterface();
>     ...
>     si->enableSimplexInterface();
>     si->getBasisStatus();
>     si->disableSimplexInterface();
>
>     si->enableSimplexInterface();
>     si->getBInvARow( );
>     si->disableSimplexInterface();
>     ...
>     //some stuff...
>  }
>}
>
>Thanks,
>Matt
>
>
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