[SCIP] The strange behavior of the CONSENFOLP callback assertion

[Abbas Omidi]

Dear Mathieu,

Many thanks for your suggestions. It seems working on the template is not
suitable to execute and check how the conshdlr works. I tried to use
another example and now the results are reasonable. However, I still have
some issues, but at the moment, it is enough for me. If it is needed, I
will open a new issue.


Thanks once again
Regards
Abbas

On Sun, Aug 6, 2023 at 7:41 AM Abbas Omidi <abb.omidi at gmail.com> wrote:

> 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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