[Scip] Problem with Conflict Analysis

[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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> >
> >
>