[SCIP] How to check and separate only integer solutions in a constraint handler?

[Mathieu Besançon]

[Resending to the whole list]

Dear Juan,
This might be a matter of the priority you set for the constraint handler.
The integrality constraint handler has a priority of 0 so if you want your
constraint handler to only receive integer solutions, its priority should
be negative.
This is explained in the TSP example, TSP/src/ConshdlrSubtour.cpp line 108
onwards:

 *  The integrality constraint handler has a check priority of zero. A
constraint handler which can
 *  (or wants) to check its constraints only for integral solutions should
have a negative check priority
 *  (e.g. the alldiff-constraint can only operate on integral solutions).

The methods you implemented seem to be the relevant ones.

Best,
Mathieu


On Sat, Apr 15, 2023 at 11:03 AM Lastra Diaz Jose <j.lastra at lectra.com>
> wrote:
>
>> Dear all,
>>
>>
>>
>> I am implementing a branch-and-Check approach to solve a 0-1 ILP model
>> and I would like to check the feasibility of integer solutions, and insert
>> a feasibility cut to separate those infeasible solutions. I have
>> implemented a constraint handler based on the TSP example, but I have not
>> understood well what callback I should implement. I have implemented the
>> four separation and enforcement callback below, as done in TSP example, but
>> when I check the solution in these callbacks, the solution is not binary.
>> Likewise, I do not know how to skip non-integer solutions in the check
>> callback.
>>
>>
>>
>> What should I do to check and separate only infeasible integer solutions?
>>
>>
>>
>> - SCIP_DECL_CONSSEPALP
>>
>> - SCIP_DECL_CONSSEPASOL
>>
>> - SCIP_DECL_CONSENFOLP
>>
>> - SCIP_DECL_CONSENFOPS
>>
>> - SCIP_DECL_CONSCHECK
>>
>>
>>
>> ObjConshdlr(scip, "overdemand", "Feasibility cuts",
>>
>>              1000000, -2000000, -2000000, 1, -1, 1, 0,
>>
>>              FALSE, FALSE, TRUE, SCIP_PROPTIMING_BEFORELP,
>> SCIP_PRESOLTIMING_FAST)
>>
>>
>>
>>
>>
>> Thank you very much for your help,
>>
>> Juan
>>
>>
>>
>> [image: cid:image001.png at 01D4B3E6.540B6570]
>>
>> *Juan J. Lastra Díaz, PhD*
>>
>> *Advanced Research department*
>>
>>
>>
>> *t **:   *+34 917 88 88 65
>>
>> *e** :   *j.lastra at lectra.com
>>
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>
> --
> Mathieu Besançon
>


-- 
Mathieu Besançon
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