Adding exactly k cuts at a root node.

[ComboProblem]

I would like to make sure for any root node that exactly k cuts are added to the root node. I have a general understanding of enabling adding cuts only at the root node from #763 and other related issues.

What I'm struggling with is how enforce "use exactly k cuts" condition. Is it possible to enforce such a condition within SCIP? If so, how does one go about doing this?

[Joao-Dionisio]

Hey @ComboProblem ! You probably want to use model.setParam("separating/maxcutsroot", k). Although this doesn't say use exactly k cuts, but rather at most k cuts. Would that be enough? For exactly k cuts, one would need to force SCIP to keep separating until that point. For this, I would play around with model.setParam("separating/maxcutsgenfactor", -1), but I'm not too sure on this one.

[Joao-Dionisio]

I think the issue is that maxcutsroot is about the number of cuts per round, and so we should also limit the number of rounds.

model.setParam("separating/maxcutsroot", 1)
model.setParam("separating/maxroundsroot", 1)                                                                                                                                                                 

[ComboProblem]

When I tried this change, it doesn't seem like that has changed the number of cuts present with the same test problem.

[Joao-Dionisio]

Ah damn, sorry for leaving you hanging @ComboProblem , I don't often check the discussion page. I'll start looking into this today!

[Joao-Dionisio]

Okay, so a couple things to try. I see that you're using forcecut=True in your code. This bypasses the parameters, and you may not want that. And secondly, when you reset the separation parameters at the root and then apply your own scip_disable_other_cuts.set, you're losing out on the parameters you set on the beginning (e.g. maxcutsroot). I don't think the handler is necessary.

[ComboProblem]

No worries about the delay. Thank you. This has helped immensely. After implementing the suggested changes, it seems that

model.setParam("separating/maxcutsroot", 1)
model.setParam("separating/maxroundsroot", k) 

add exactly "k" cuts at the root node.