[Scip] Eliminating model constraints following branching

[Ambros Gleixner]

Hi Steve,

 > During the solution process, some of these constraints are
 > added to the problem.

precisely speaking you probably mean "the LP relaxation of some of these 
constraints are added to the problem", right?

You can use the SCIP method SCIPdelConsLocal() to disable the 
constraint's separation, enforcing, and propagation capabilities at the 
current node and all subnodes.

I think you cannot directly force the corresponding rows to be removed 
from the LP.  If I understand you correctly, this is what you would want 
to do, right?  Can you tell us more about your motivation for this?  Are 
they redundant after the branching decision you make?

If you declare the constraints as "removable" when creating them, their 
LP relaxation will be subject to ageing, i.e., they are removed if they 
are not tight for some time.  By playing with the advanced parameter 
lp/rowagelimit you can control how aggressively this is applied.  Maybe 
this can achieve the desired effect?

Are the constraints from a specific constraint handler?

Hope that helps, let us know!

Ambros




Am 15.02.2013 04:40, schrieb Stephen J Maher:
> Hi all,
>
> I was just wondering whether it was possible to locally remove models
> constraints from a node when the branching decisions are made. My goal
> is to reduce the size of my problem by removing model constraints for
> each subproblem that is created in the branch-and-bound tree.
>
> At the moment I start the model with only a subset of all constraints
> initially included in the LP. This is done by setting the initial flag
> to false. During the solution process, some of these constraints are
> added to the problem. When branching is performed, I would like to
> remove the constraints that were added and start the solving again.
>
> You help is appreciated.
>
> Cheers,
>
> Steve
>

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