[Scip] Fractional solution, pruned node

[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,


-- 
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Cristina Nuñez
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