[Coin-discuss] Problem in Osi->branchAndBound() (with Clp as linear solver)

[mathieu lacroix]

Hi,

I use COIN (OSI/CLP) in linear optimization lesson. I need to solve a 
little integer linear problem so I use  the osi method 
branchAndBound().  I thank you a lot to implement the method with the 
linear solver Clp. It work well but  there  still exists a little  
mistake. Indeed, you can't run the branchAndBound method more than once 
on the same OSI object. In this case, it throws an exception. (One 
reason is that when you write the problem in a lp file after running 
once branchAndBound method, the lower and upper bounds of the variables 
are not the initial ones but the one of the optimal solution. But, even 
you change those bounds (setColLower(...) and setColUpper(...)), it 
doesn't work and throws an exception. I think that it is because in a 
more general form, at the end of the branchandbound method, the initial 
data are substituted by other generated and used by the branchAndBound() 
method).
Or, I have to solve the integer linear problem of 4 variables and one 
constraint several times by changing each time only objective 
coefficients. The only way to do it is to construct each time a new 
problem from scratch or to apply the method loadProblem(...), even if it 
is exactly the same problem you want to solve twice.

Thank you in advance for your answer,

Best regards,

Mathieu LACROIX



-- 
Mathieu LACROIX
mathieu.lacroix at isima.fr
Université Blaise Pascal - Clermont Fd II
Laboratoire LIMOS
Bâtiment ISIMA - Bureau D112
Complexe scientifique des Cézeaux
63 177 Aubière, Cedex - France
Tel : 04.73.40.79.48
Fax : 04.73.40.76.39