Originally posted by: mkadem

Hi to all,

i want to switch off some methods that cplex uses in the node 0. In fact, i found some instances where the time limit is reached (i put half an hour) and cplex doesn't starting branching (node 0). However, the relaxed version is solved in 7 seconds. i switch off cuts generations and others parameters:

            cplex.setParam(IloCplex::Probe, -1);

            cplex.setParam(IloCplex::IntParam(2132), -1);

            cplex.setParam(IloCplex::CutPass,-1);

            cplex.setParam(IloCplex::Cliques,       -1);

            cplex.setParam(IloCplex::Covers,        -1);

            cplex.setParam(IloCplex::FlowCovers,    -1);

            cplex.setParam(IloCplex::FlowPaths,     -1);/

            cplex.setParam(IloCplex::GUBCovers,     -1);

            cplex.setParam(IloCplex::ImplBd,        -1);

            cplex.setParam(IloCplex::MCFCuts,       -1);

            cplex.setParam(IloCplex::MIRCuts,       -1);

            cplex.setParam(IloCplex::FracCuts,      -1);

            cplex.setParam(IloCplex::DisjCuts,      -1);

            cplex.setParam(IloCplex::ZeroHalfCuts,  -1);//

but the problem persists. what i can do ??

thanks 

In order to disable all cuts it may be easier to just limit the number of cutting plane passes, see CPX_PARAM_CUTPASS. Another thing that may consume time at the root node are heuristics. You can disable heuristics via CPX_PARAM_HEURFREQ. Can you show us the log output of such a lengthy root node solve? It should tell where time is spent.

Note that you can re-enable all those things for B&B using the following strategy:

1. Modify parameters so that the root node supposedly solves quickly.
2. Set the node limit to 1.
3. Solve. This will stop right after the root node.
4. Change parameters back to original values.
5. Clear the node limit.
6. Solve. This should start from where the previous solve stopped, so after the root node.