[SCIP] question on branching

[Tristan Gally]

Dear James,

if you only want to branch on this particular variable, it shouldn't be 
necessary to get all branching candidates. You could write a branching 
rule where you just check the bounds of your particular variable (you 
can get it via SCIPfindVar()), in case they are equal, you return 
SCIP_DIDNOTRUN to skip your branching rule and continue with SCIP's own 
ones. Otherwise you directly call SCIPbranchVar() to branch on your 
variable.

If you wanted to use the SCIPgetPseudoBranchCands() callback (which, as 
I said, shouldn't be necessary), you would get a list of all possible 
candidates to iterate over and select one based on any criterion of your 
choice. In your case, you could iterate over the list and check whether 
any of the variables is named "x".

Best,
Tristan

On 02/16/2017 04:13 PM, James Cussens wrote:
> Dear SCIPers,
>
> I have a problem which includes a particular integer variable (call it 
> x) which I always want to branch on even if it is integral and other 
> binary/integer variables are fractional - I would only branch on any 
> other variable if x were fixed. As for how to branch on this variable, 
> the BRANCHEXECPS approach described here:
> http://scip.zib.de/doc/html/BRANCH.php
> is exactly what I am looking for.
>
> Giving this x variable maximal branching priority does not work, since 
> if (as is normally the case) there is an LP solution with some 
> fractional variables not including my x, then x will not be branched on.
>
> So it looks like I need to write my own (simple) branching rule where 
> the BRANCHEXECLP callback grabs branching candidates 
> using SCIPgetPseudoBranchCands rather than SCIPgetLPBranchCands. 
> However, looking at the code in branch.c it appears 
> that SCIPgetPseudoBranchCands returns branching candidates without 
> taking variable priority into account.
>
> Is that correct?
>
> Best wishes,
>
> James
>
> -- 
> James Cussens
> Dept of Computer Science &
> York Centre for Complex Systems Analysis
> Room 326, The Hub, Deramore Lane            Tel    +44 (0)1904 325371
> University of York  Fax  +44 (0)1904 500159
> York YO10 5GE, UK http://www.cs.york.ac.uk/~jc 
> <http://www.cs.york.ac.uk/%7Ejc>
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>
>
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