Aritifical variables, was: Re: [Coin-lpsolver] Parametric Analysis using CLP + OSI

[John J Forrest]

Paulo,

A valid basis may need artificial variables.  For instance if two rows of 
the matrix are identical an artificial must be in basis.

John Forrest



"Paulo J. S. Silva" <pjssilva at ime.usp.br> 
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03/08/2005 01:13 PM

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Subject
Aritifical variables, was: Re: [Coin-lpsolver] Parametric Analysis using 
CLP + OSI







> Paulo, 
> 
> It depends how you are picking up basis information.  With a problem
> of  n columns and m rows Clp numbers the structural variables (column)
> 0 through n-1 and the artificial/slack variables n through n+m-1. 
> 
> John Forrest 


In that case what I do is:

s.initialSolve()
s.enableSimplexInterface(True)
s.getBasics(basics)

If I look at basics I get a 469 in the basis. My problem has 460
variables and 198 rows. Hence, using your explanation, it looks like
there are still artificial variables in the basis. 

Is there a way to pick up a "valid" basis, using only structural
variables? 

Paulo
-- 
Paulo José da Silva e Silva 
Professor Assistente do Dep. de Ciência da Computação
(Assistant Professor of the Computer Science Dept.)
Universidade de São Paulo - Brazil

e-mail: pjssilva at ime.usp.br        Web: http://www.ime.usp.br/~pjssilva

Teoria é o que não entendemos o    (Theory is something we don't)
suficiente para chamar de prática. (understand well enough to call) 
                                   (practice)



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