[Scip] Problem with Conflict Analysis

[Ambros Gleixner]

That means you may use the tighter bound when computing a reason for the 
propagation.  This is preferable since it can give you a smaller reason 
than the bound that was known when the propagation was actually 
performed; smaller meaning a reason with less changes compared to the 
global bounds now.

Hope that helps,

ambros



Am 10.10.2013 17:44, schrieb Alexander Schnell:
> Hi Ambros,
>
> yes, the lower bound is tighter.
>
> Alex
>
>
>
> On Thu, 2013-10-10 at 17:20 +0200, Ambros Gleixner wrote:
>> Hi Alexander,
>>
>> is the value of the variable responsible for the lower bound change
>> tighter than the value that was stored in inferinfo?
>>
>> I think this could be correct, if global bound changes have occured in
>> the meantime.  Can somebody confirm this?
>>
>> Ambros
>>
>>
>>
>>
>> Am 10.10.2013 17:15, schrieb Alexander Schnell:
>>> Dear Marc,
>>>
>>> my problem is not about the variable
>>> for which the lower bound change is applied (infervar) but about the
>>> variable responsible for the lower bound change
>>> (i.e. the lower bound of this variable).
>>>
>>> For this variable SCIPvarGetLbAtIndex(...,...,TRUE) and
>>> SCIPvarGetLbAtIndex(...,...,FALSE) are the same values.
>>>
>>> I integrate the lower bound of this variable as an integer inferinfo
>>> in the function SCIPinferVarLbCons(). Moreover, if I query
>>> the lower bound of this variable in the CONS_RESPROP function
>>> by SCIPvarGetLbAtIndex(), this does not correspond to the
>>> inferinfo value.
>>>
>>> Note, that I can be sure that the value returned
>>> from SCIPvarGetLbAtIndex() is integer (I tested it by
>>> SCIPisFeasIntegral()).
>>>
>>> Best regards,
>>> Alexander
>>>
>>>
>>>
>>>
>>>
>>>
>>> On Thu, 2013-10-10 at 16:09 +0200, Marc Pfetsch wrote:
>>>>
>>>> Dear Alexander,
>>>>
>>>> the function SCIPvarGetLbAtIndex() contains a parameter in which you can
>>>> specify whether the bound change in questions has already been applied.
>>>> To which value have you set this value? In principle, you should be able
>>>> to reconstruct the bound change at that time (using infervar and the
>>>> above function).
>>>>
>>>> Please also check whether the bound change via SCIPinferVarLbCons()
>>>> actually changed the bound (check return values infeasible and tightened).
>>>>
>>>> You can look at other examples of conflict resolution, e.g.,
>>>> cons_linearordering.c in examples/LOP. Please note that implementing
>>>> conflict resolution always is a tricky thing.
>>>>
>>>> If this does not explain the problem, we would need more details from
>>>> you in order to be able to reconstruct the problem. Possibly off this
>>>> list ...
>>>>
>>>> Best
>>>>
>>>> Marc
>>>>
>>>>
>>>> On 10.10.2013 15:32, Alexander Schnell wrote:
>>>>> Dear SCIP team,
>>>>>
>>>>> I implemented a Constraint Handler for a special
>>>>> project scheduling problem.
>>>>>
>>>>> In the CONS_RESPROP function, I try to explain the bound
>>>>> changes processed through the propagation algorithm implemented in
>>>>> the CONS_PROP function.
>>>>>
>>>>> In the function for the explanation generation, I observed a problem
>>>>> with the function SCIPvarGetLbAtIndex(...):
>>>>>
>>>>> In the propagation algorithm, the lower bound is propagated with
>>>>> the function SCIPinferVarLbCons(). I integrate the integer lower bound
>>>>> of the variable responsible for the processed bound change as an
>>>>> inferinfo in this function.
>>>>>
>>>>> In the CONS_RESPROP function, I compare the latter value with the actual
>>>>> lower bound of the responsible variable given by
>>>>> SCIPvarGetLbAtIndex(...) at the given bound change index.
>>>>>
>>>>> My problem is that these values are not the same, which should not be
>>>>> the case in my understanding.
>>>>>
>>>>> Thank you in advance for your help.
>>>>>
>>>>> Best regards,
>>>>> Alexander Schnell
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> Scip mailing list
>>>>> Scip at zib.de
>>>>> http://listserv.zib.de/mailman/listinfo/scip
>>>>>
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>>>
>>>
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>>
>
>

-- 
____________________________________________________________
Ambros M. Gleixner
Zuse Institute Berlin - Matheon - Berlin Mathematical School
http://www.zib.de/gleixner