[Scip] simple rounding and xor constraints

[Ambros Gleixner]

Hi James,

I am not an expert here, but after a quick look at
heur_simplerounding.c, I would suppose the heuristic is called during
the LP pricing loop and detects -- as you suggested -- that the current
LP solution is integral.

You could check this by adding

   #define SCIP_DEBUG

to the top of heur_simplerounding.c.  This should give you an output
line "executing simple rounding heuristic: X fractionals" with X=0 if
our guess is correct and print the solution.

ambros



Am 14.03.2011 13:53, schrieb James Cussens:
> I have a problem where all the variables are binary and each variable 
> participates in exactly one xor constraint. Each xor constraint states 
> that exactly one of a certain collection of binary variables is true. 
> (There is also another constraint implemented by my own constraint 
> handler, but I don't think that's relevant).
> 
> I've noticed that simple rounding finds valid primal solutions. This 
> seems a little odd since I think xor down- and up- locks each variable. 
> My guess is that wholly integral solutions are being found during LP 
> solving - does this seem right?
> 
> James
> 

-- 
____________________________________________________________
Ambros M. Gleixner
Zuse Institute Berlin - Matheon - Berlin Mathematical School
http://www.zib.de/gleixner