How to fully disable automatic node fathoming in PySCIPOpt?

[ICSRicotero]

Hi all,

I'm implementing a custom Branch-and-Bound logic using PySCIPOpt. While I can manually prune nodes (e.g., by returning SCIP_RESULT.CUTOFF from my custom plugins), I want exclusive control over when fathoming occurs.

Currently, SCIP automatically prunes nodes in the background via:

Bound: LP lower bound exceeds the cutoff bound.

Infeasibility: LP relaxation or domain propagation proves infeasibility.

Is there a way to completely disable these automatic internal fathoming mechanisms so my logic is the sole trigger?

If no global parameter exists, is the best workaround to use Model.setObjlimit(float('inf')) to prevent bound pruning, and turn off all propagators to prevent infeasibility pruning?

Thanks!

[Joao-Dionisio]

Hey @ICSRicotero ! I don't think there's a single parameter for this, but what may help is the following.

1. Don't set an objective to the problem, but rather handle it yourself. That way, nodes are not pruned by bound, but you need to add a constraint handler that rejects any found solutions, so that the search keeps going.
2. While it's not possible to disable infeasibility pruning (I couldn't find a way, at least), you can disable components that detect infeasibility:

model.setPresolve(SCIP_PARAMSETTING.OFF)
model.setHeuristics(SCIP_PARAMSETTING.OFF)
model.setSeparating(SCIP_PARAMSETTING.OFF)
model.setParam("propagating/maxrounds", 0)
model.setParam("propagating/maxroundsroot", 0)
model.setParam("conflict/enable", False)
model.setParam("misc/allowstrongdualreds", False)
model.setParam("misc/allowweakdualreds", False)

I may have missed some, but beware that this will have an impact on solving time. For the branch-and-bound tree traversal, I then suggest implementing a node selector.

This is all super hacky, can you think of a better way to do this @DominikKamp ?

[DominikKamp]

If the LP solver finds a primal solution, it will cut off the current node, so one would also need to disable LP solving with lp/solvefreq = -1 and all heuristics with emphasis:heuristics off or maybe just not include any default plugins to prevent solving anything. Trivial cutoffs will always happen since a node can not be processed further otherwise. Maybe try to increase priority of the custom plugins to prune before SCIP will do.