[SCIP] presolving query

[Ambros Gleixner]

Hi James,

the presolving step you mention is very basic und so you are right to 
expect it from SCIP.  The linear and the setppc constraint handlers 
implement it, however, it seems to be missing in the logicor constraint 
handler.

Also the PaPILO library behind presol_milp.cpp should detect it.  Can it 
be that you are running without PaPILO?

You could use setppc (or general linear) constraints instead, but I 
assume this has other negative implications?  If you are stuck with 
logicor constraints, then I don't see a simple parameter switch to 
enable this presolving step.  (Except possibly activating PaPILO.)

Best,
Ambros




Am 14.06.2023 um 09:17 schrieb James Cussens:
> Hi all,
> 
> I have a problem which after presolving contains the following vars and 
> conss (among a bunch of other stuff):
> 
> OBJECTIVE
>    Sense            : minimize
>    Offset           : -62.7528704623564
> VARIABLES
> ...
>    [binary] <t_pa#1>: obj=8.51719319141624, global bounds=[-0,1], local 
> bounds=[-0,1]
>   ....
>    [binary] <t_v#0>: obj=33.6097102878493, global bounds=[-0,1], local 
> bounds=[-0,1]
>   ...
> CONSTRAINTS
> ...
> [logicor] <cluster_or>: logicor(<t_v#0>[B],<~t_pa#1>[B]);
> ...
> 
> The variable t_v#0 appears only in the above logicor constraint. So 
> clearly in any optimal solution t_pa#1 = t_v#0. So I was expecting t_v#0 
> and its constraint to be
> removed and the objective coefficient of t_pa#1 to be increased by 
> 33.609. But this isn't happening. Is there perhaps some presolving 
> parameter I could set to make this happen?
> 
> It's not a big deal for me to do this presolving "manually" as I 
> construct the problem instance but it would be nicer if it "just happened".
> 
> James
> 
> James Cussens
> Room MVB 3.26
> Dept of Computer Science, University of Bristol
> Phone: +44 (0)117 455 8723
> https://jcussens.github.io/ <https://jcussens.github.io/>
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