[Scip] Fractional solution, pruned node

[Gerald Gamrath]

Dear Christina,

sorry for the late reply, but we were quite busy in the last weeks.

There might be different reasons for this behavior.

1) Does your pricing callback compute a lower bound and sets the 
lowerbound pointer accordingly? If this is higher than the cutoff bound, 
the node will be cut off.

2) Perhaps the propagation already detected infeasibility? Are you sure 
that you perform pricing at this node?

3) Are all your variables created by pricing and all constraints marked 
to be modifiable? Otherwise, the enforcement might also detect 
infeasibility of an unmodifiable constraint.

Best,
Gerald

Am 19.02.2015 um 15:27 schrieb Cristina Núñez del Toro:
> Dear all,
>
> I am currently implemented a Branch&Price algorithm. For my problem, I 
> have 3 types of variables, say "x","y" and "z". I have just finished 
> my on branching rule that implies to only branch on the "z" variables. 
> Apparently, everything goes ok; I mean, everytime SCIP enters to the 
> branchexeclp routine, it looks for the most fractional "z" variable 
> and do branch on it. However, I have noticed that a certain point of 
> the algorithm, after finishing the pricing loop, SCIP "skips" (sorry 
> for the joke) the branching phase (the node is cutted off/pruned), I 
> mean, it does not enter to any branching callback method and goes 
> directly to the handler constraint to propagate another node. As far I 
> understand, this would be of course a normal behaviour if, after 
> finishing the pricing stage :
>
> a) the objective value of the current LP is greater or equal than the 
> incumbent,
> b) the current LP solution is an integer solution,
> c) the current LP solution is an integer solution and it is optimal.
>
> However, I found a pruned node with a fractional LP solution (inluding 
> some "z" variables with fractional value) but with the objective value 
> strictly lower than the incumbent.
>
> Is there any reason for expecting this?
>
> Thanks in advances,
>
> Best regards,
>
>
> -- 
> ---
> Cristina Nuñez
>
>
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