[Coin-discuss] Branch and price restore feasibility dual rays

[Jakob Puchinger]

hi matthew,

it worked! (like that: CPXdualfarkas(env_, getMutableLpPtr(), ray, NULL);)
thank you very much,

jakob

On Sat, 24 Jul 2004 coin-discuss-request at www-124.southbury.usf.ibm.com wrote:

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>    1. Re: Branch and price restore feasibility dual rays (Matthew Galati)
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> --__--__--
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> Message: 1
> Date: Sat, 24 Jul 2004 08:29:27 -0400
> From: Matthew Galati <magh at lehigh.edu>
> To: coin-discuss at www-126.southbury.usf.ibm.com
> Subject: Re: [Coin-discuss] Branch and price restore feasibility dual rays
> Reply-To: coin-discuss at www-124.ibm.com
> 
> Hi Jakob,
> 
> I brought up the same issue back in December.
> http://www-124.ibm.com/pipermail/coin-discuss/2003-December/000730.html
> 
> I don't use CPX much, so I never bothered investigating this more. But, 
> if I recall, I think the OsiCpx getDualRays is wrong.
> 
> Try switching the OsiCpxSolverInterface::getDualRays to use CPXs direct 
> call:
> CPXdualfarkas(getEnvironmentPtr(), getLpPtr(), ray, NULL);
> 
> I think you also need to negate it, as this is what BCP expects:
> transform(ray, ray + m, ray, negate<double>())
> 
> Let me know if this works and if not, send a small isolated example.
> 
> COIN folks, can we switch to a version of mailman that provides 
> searchable archives?
> 
> Matthew
> 
> 
> 
> >hi,
> >
> >I am looking again at my problem from february, where I cannot use the 
> >dual ray from OsiCpxSolverInterface to generate a variable breaking 
> >infeasiblity, whereas the ray from OsiClpSolverInterface works well.
> >Until now I used Clp which worked well,
> >but I would like  to compare to  cplex.
> >
> >I am applying B&P to a 2D bin packing problem, each variable is 
> >a pattern, and each row corresponds to an item (it guarantees that the 
> >item is used). 
> >OsiClp returns a dual ray having one entry set to a high value, and the 
> >others to zero, it therefore gives me the index of a missing item of 
> >the solution (i.e. adding a pattern containing this item can restore 
> >the feasibility).
> >OsiCpx returns a dual ray having several entries set to 1, or 0.5, but
> >the entries correspond to items which are allready available in the 
> >solution, therefore I cannot generate a variable breaking infeasibility
> >using this information.
> >
> >thank you for your answers (also for the answers from february)!
> >
> >best wishes
> >jakob puchinger  
> >_______________________________________________
> >Coin-discuss mailing list
> >Coin-discuss at www-124.ibm.com
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> >  
> >
> 
> -- 
> Matthew Galati -- Optimization Developer
> SAS Institute -- Analytical Solutions / Operations R & D
> Office R4112 O: 919-531-0332 F: 919-677-4444
> URL: http://sagan.ie.lehigh.edu/mgalati/ 
> 
> 
> 
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