Why does CPLEX spend so much time solving root LP relaxation?

Why does CPLEX spend so much time solving root LP relaxation?

For example, you may find that CPLEX spends most of its time solving the root LP relaxation. In that case, consider setting the startalgorithm parameter to a non default value. Or, you may find that CPLEX spends a lot of time applying the node heuristic, but that the heuristic never finds a good feasible solution.

Which is the best way to improve CPLEX performance?

Probing can dramatically improve performance, although it may also consume significant amounts of time. It helps on problems with binary variables rather than general integer variables. Starting with CPLEX 10.0, the probing time limit parameter can help when aggressive levels of probing are effective but take too long.

Which is branch and bound approach does CPLEX apply?

Cplex applies various approaches to those problems, such approaches as barrier algorithms or branch and bound algorithms. Notably, in the branch and bound approach, there is no theoretical guarantee about the complexity of such a problem. Consequently, solution of such a problem (that is,…

What to look for in a CPLEX node log?

CPLEX provides a node log that shows the progress of its branch and bound algorithm on a MIP. Be sure to look at the node log to help locate the performance bottleneck.

Why does CPLEX have little time for branching?

If most of the time is spent at the root node, CPLEX has very little time for branching, so the benefit of more informed branching decisions at the child nodes may not be worth the cost of the root node calculations. Note that this won’t always be the case.

When to turn off the node heuristic in CPLEX?

Or, you may find that CPLEX spends a lot of time applying the node heuristic, but that the heuristic never finds a good feasible solution. In that case, turn the node heuristic off. Look at the MIP Troubleshooting section of the CPLEX User Manual for additional examples and information.

What are the new features of CPLEX 9.0?

Make good use of CPLEX’s MIP Start, RINS heuristic and solution polishing features . CPLEX 9.0 and 10.0 added new features that can help find feasible solutions much faster. Support of partial and infeasible MIP starts, solution repair, the RINS heuristic, and solution polishing are all very useful features by themselves.

What should the MIP display parameter be in CPLEX?

By setting the MIP display parameter to values ranging from 2-5, you can get detailed information about the progress of the MIP optimization in the CPLEX node log. This information often sheds light on the cause of slow performance. For example, you may find that CPLEX spends most of its time solving the root LP relaxation.

Why does CPLEX have a slow start time?

This information often sheds light on the cause of slow performance. For example, you may find that CPLEX spends most of its time solving the root LP relaxation. In that case, consider setting the startalgorithm parameter to a non default value.