Branching mechanism in B&P using SCIP

0
votes

I'm implementing a branch and price algorithm in c using SCIP.

Question: To call the branching mechanism, I use the basic BRANCHEXECLP mechanism. How does SCIP know when to branch? When the current relaxation solution has non-integer solutions, right? I don't have to tell SCIP to invoked the branching mechanism for this case, right?

I'm asking because (for the most part) my B&P algorithm is working well. But, at some point it reaches a node corresponding to the dual bound solution. After solving the pricing problem (and no columns are attractive to enter the master problem), the relaxation solution at this node contains non-integer solutions, but the branching mechanism is not invoked. The run just quits. Any idea as to what is going on here?

Thanks, Rob Curry

1
scip

1 Answers

1
votes

I guess you checked during pricing that there are fractional variables in the current LP solution?

And the dual bound at that node equals the global dual bound? Did you mark your objective to only have integral values? In that case, if the dual bound is close enough to the primal bound that rounding it up gives the same number, SCIP will just cut off the node. Perhaps also SCIP found a new solution after your pricing which was immediately proven to be optimal by the current global dual bound? SCIP automatically runs some simple rounding heuristics after each solved LP in the pricing loop.