[Scip] Problem with Conflict Analysis

[michael.winkler at zib.de]

Hi Alex,

> Hi Ambros,
>
> thank you again for your answer. This is now clear for me.
> Now I have the same problem with an upper bound.
>
> The upper bound of a variable at the time of the bound change
> is 1. When I try to explain the bound change the upper bound
> of the same variable is 0 (with SCIPvarGetUbAtIndex()).
>
> But the global upper bound of this variable is 1 and not 0.
> I also queried the value var->glbdom.lb and var->glbdom.ub
> of the same variable.
>
> Is it normal that var->glbdom.lb = 1 and var->glbdom.ub = 0?
> Note that the domain of this variable is {0,1}.
>

you say that the global upper bound is not 1 but zero and now you say
var->glbdom.ub = 0; can you please check again, what happens.

Contradicting global bounds should be not possible. Did you try to run
your program with valgrind; it can find invalid writes and many more
things. (www.valgrind.org)

Best, Michael

> Thanks,
> Alex
>
>
>
> On Thu, 2013-10-10 at 18:46 +0200, Ambros Gleixner wrote:
>> Hi Alex,
>>
>> this is a good remark.  The point is that it is a tighter *global*
>> bound.  Hence in your example,  if s has a lower bound of 5, the reasons
>> "s >= 3" and "s >= 5" are equivalent: an empty list of bound changes.
>> (I.e., t >= 6 should be globally valid.)
>>
>> Thanks,
>>
>> Ambros
>>
>>
>> PS: Maybe you want to confirm for your safety that the tighter value
>> from SCIPvarGetLbAtIndex() is the same as SCIPvarGetLbGlobal().
>>
>>
>>
>> Am 10.10.2013 18:31, schrieb Alexander Schnell:
>> > Thank you for this information. This helped very much but
>> > I have another remark.
>> >
>> > I agree on the part that the tighter bound may be used
>> > as a reason for the propagation, but i think the old lower
>> > bound would lead to a better explanation:
>> >
>> > assume that s >= 3 lead to the bound change of t >= 6
>> > and the tighter global lower bound 5 is introduced for s.
>> >
>> > Then the old explanation s>= 3 -> t >= 6 is stronger than
>> > s>= 5 -> t >= 6.
>> >
>> > Alex
>> >
>> >
>> > On Thu, 2013-10-10 at 17:50 +0200, Ambros Gleixner wrote:
>> >> 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
>> >>>>>>>
>> >>>>>>>
>> >>>>>>>
>> >>>>>>>
>> >>>>>>>
>> >>>>>>>
>> >>>>>>>
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>> >
>> >
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