[SCIP] The strange behavior of the CONSENFOLP callback assertion

[Abbas Omidi]

Dear Mathieu,

Thank you so much. Please, let me check and reach out to you if I have any
questions.

Best regards
Abbas

On Sat, Aug 5, 2023 at 6:32 PM Mathieu Besançon <mathieu.besancon at gmail.com>
wrote:

> 1. The assert is specific to the test and should not be used as a template
> for a constraint handler.
> If your check returns SCIP_FEASIBLE, the constraint handler has no reason
> to enforce the constraint on the LP solution (aka to call consenflp),
> because there is nothing to do to make the constraint feasible.
>
> 2. The priorities should be explained on the constraint handler page:
> https://www.scipopt.org/doc/html/CONS.php
>
> for 3, maybe check a realistic constraint handler, such as
> PySCIPOpt/examples/finished/lotsizing_lazy.py
>
>
> Hope this helps,
> Mathieu
>
>
>
>
>
> On Fri, Aug 4, 2023 at 8:27 PM Abbas Omidi <abb.omidi at gmail.com> wrote:
>
>> Dear Mathieu,
>>
>> Thank you so much for your informative comments. Now, it makes sense to
>> the *price-and-cut loop *and also, what is the difference between
>> *consenfolp/**consenfops.*
>>
>> Is the solution feasible for your constraint? If yes, you can just use
>>> SCIP_FEASIBLE as a result.
>>
>>
>> Let me explain more on what I am trying to do. I have tried using a
>> simple example and already mentioned the template here
>> <https://github.com/scipopt/PySCIPOpt/blob/master/tests/test_conshdlr.py>
>> to investigate how *conshdlr* works and how behaves again adding the
>> custom constraints. The problem I am using has an optimal solution and also
>> I defined SCIP_FEASIBLE as a result in both *conscheck *and *consenflp*.
>> After declaring the optimization model, I added *writeProblem* method to
>> see what exactly is added to the model. Then I called the following method
>> to include *conshdlr* :
>>
>> conshdlr = MyConshdlr(shouldtrans=True, shouldcopy=False)
>>> s.includeConshdlr(conshdlr, "PyCons", "custom constraint handler
>>> implemented in python",
>>> sepapriority= 1, enfopriority= 1, chckpriority= 1
>>> )
>>
>>
>> Then I created and added three custom constraint handlers still based on
>> the original problem constraints by using:
>>
>> cons1 = s.createCons(conshdlr, "cons1name")
>>> ids.append(id(cons1))
>>
>>
>>> conshdlr.createData(cons1, 10, "cons1_anothername")
>>
>>
>>> s.addPyCons(cons1)
>>
>>
>> By running the code, it shows the assertion errors on --> 143 assert
>> "consenfolp" in calls.
>> Also, the write method shows the following rows added, but it cannot
>> convert that into a readable format:
>>
>> constraint handler <PyCons> cannot print requested format
>>> \   [PyCons] <cons1name>: ;
>>> constraint handler <PyCons> cannot print requested format
>>> \   [PyCons] <cons2name>: ;
>>> constraint handler <PyCons> cannot print requested format
>>> \   [PyCons] <cons3name>: ;
>>
>>
>>
>> My questions are:
>> 1)  Why do I have an assertion error on *consenflp *while the problem
>> has an optimal solution?
>> 2) How can I find the priority numbers and their definitions of
>> *sepapriority*, *enfopriority*, and *chckpriority*? (I cannot find
>> related documents)
>> 3) I am not sure why I need to redefine the constraints by createCons,
>> createData, and addPyCons respectively. I just tried to use the
>> template format, and this is why I asked about adding data. If I am doing
>> wrong pleaes, correct me?
>>
>>
>> All the best
>> Regards
>> Abbas
>>
>> On Thu, Aug 3, 2023 at 7:33 PM Mathieu Besançon <
>> mathieu.besancon at gmail.com> wrote:
>>
>>> Dear Abbas,
>>>
>>> 1. The price-and-cut-loop happens before the constraint handler is
>>> called, this corresponds to the step where the LP relaxation has been
>>> solved, and the rounds of cuts (from separator plugins) have already
>>> happened.
>>>
>>> 2. consenfoXYZ acts on a primal solution by adding a constraint, cut, or
>>> something else. In contrast, the check function only computes whether a
>>> violation of the constraint represented by the constraint handler is
>>> present at the current solution, and returns whether the solution is
>>> feasible or infeasible.
>>> https://www.scipopt.org/doc/html/CONS.php
>>>
>>> 2 bis. I am not sure to understand what you mean by this one. Is the
>>> solution feasible for your constraint? If yes, you can just use
>>> SCIP_FEASIBLE as a result. If this solution is not feasible, then you can
>>> do one of the actions detailed in the documentation page linked above. If
>>> the only possible thing is determining the current solution as infeasible,
>>> then the ENFO constraint can use a result SCIP_INFEASIBLE.
>>>
>>> 3. I don't think create data is necessary for a constraint handler but
>>> not sure on this one.
>>>
>>> Best,
>>> Mathieu
>>>
>>>
>>> On Sat, Jul 29, 2023 at 9:05 AM Abbas Omidi <abb.omidi at gmail.com> wrote:
>>>
>>>> Dear support team,
>>>>
>>>> I am working on the problem, and I am willing to use SCIP's*onshdlr*
>>>> callback, preferably PySCIPopt, to check how the constraints might be
>>>> added to the model. The problem I have is a simple linear program, MILP,
>>>> that is solved optimality. I sum up my questions as follows and am
>>>> wondering if, you can advise me.
>>>>
>>>> 1) As the definition of *consenfolp/consenfops *is very specific and
>>>> contains the term *price-and-cut loop*, What does the price-and-cut
>>>> loop mean?
>>>>
>>>> 2) What is the difference between *consenfolp/consenfops *and
>>>> *conscheck* when applied to the model?
>>>>
>>>> 2) As my problem has a primal feasible solution, actually optimal one,
>>>> and already other callbacks seem to work fine, how is it possible to reject
>>>> the constraints/solution by *consenfolp/consenfops*?
>>>>
>>>> 3) Is it still necessary to use *conshdlr.createData* when we want to
>>>> add the constraint?
>>>>
>>>>
>>>> (The link <http://listserv.zib.de/pipermail/scip/2023-July/004687.html>
>>>> to my previous post)
>>>> Best regards
>>>> Abbas
>>>> _______________________________________________
>>>> Scip mailing list
>>>> Scip at zib.de
>>>> https://listserv.zib.de/mailman/listinfo/scip
>>>>
>>>
>>>
>>> --
>>> Mathieu Besançon
>>>
>>
>
> --
> Mathieu Besançon
>
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