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I'm solving the VRP with Scip and want to choose the algorithm. In some of my instances, Scip solves the problem without the branch-and-bound tree in the root node; here I think cutting planes are executed. Cplex for example can choose prim Simplex or dual Simplex etc. to solve the Problem in this case.

Is there a possibility in Scip too? I use the parameters lp/initalgorithm=b (barrier) and lp/resolvealgorithm=b to make sure, in the branch-and-bound tree only this algorithm is used. But when Scip solves the problem in the root node, these parameters change nothing.

Thanks for your help!

Jack
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So if I understand you correctly you want to always use barrier to solve the LP relaxations of your problem?

You need to make sure that the LP solver you are using supports this. If you use SoPlex as the LP solver in SCIP it does not have a barrier algorithm implemented and will fallback to solving with dual Simplex instead.

The LP solvers that support barrier are Cplex, Xpress, Gurobi, Mosek, and CLP

Leon
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  • Yes, right. I use SoPlex as the LP solver and didn't know, there is no barrier algorithm, sorry. But it should work with primal Simplex or dual Simplex in SoPlex, right? – Jack Jun 15 '21 at 14:46
  • Yes it will work. It will not hard-set it to primal/dual, however. In case of fails, SCIP will change the algorithm. Also, SoPlex is a bit of a special case in that it can also switch the algorithm durin the LP solve, so it might start with primal but switch to dual during the solve. – Leon Jun 15 '21 at 21:36
  • Okay, thanks! And there is no way to hard-set it I guess? – Jack Jun 16 '21 at 06:58
  • I don't think so, no. – Leon Jun 16 '21 at 13:22