ILOG CPLEX 11.0 User's Manual

In a larger conflict, you can selectively display constraints or bounds on variables by usingthese commands to specify a range of rows or columns:display conflict constraintsdisplay conflict variablesYou can also write the entire conflict to a file in LP-format to browse later by using thecommand (where modelname is the name you gave the problem):write modelname.clpInterpreting ConflictIn those results, you can see that c8, the constraint mentioned by presolve, is indeed afundamental part of the infeasibility, as it directly conflicts with one of the skill constraints.In this example, with so many people away at training, the skill set in c2 cannot be covered.Perhaps it would be up to the judgment of the modeler or management to decide whether torelax the skill constraint or to reduce the number of people who will be away at trainingduring this period, but something must be done for this model to have a feasible solution.Deleting a ConstraintFor the sake of explanation, assume that a decision is made to cancel the training in thisperiod. To implement that decision, try entering this command:change delete constraint c8Now re-optimize. Unfortunately, even removing c8 does not make it possible to reach anoptimum, as you can see from these results of optimization:Constraints 'c5' and 'c9' are inconsistent.Presolve time = 0.00 sec.MIP - Integer infeasible.Current MIP best bound is infinite.Solution time = 0.00 sec. Iterations = 0 Nodes = 0Perhaps presolve has identified a source of infeasibility, but if you run the conflictcommand again, you will see these results:Refine conflict on 13 members...Iteration Max Members Min Members1 12 02 9 03 6 04 4 05 3 06 3 17 3 28 3 3Minimal conflict: 2 linear constraint(s)1 lower bound(s)0 upper bound(s)Conflict computation time = 0.00 sec. Iterations = 8ILOG CPLEX 11.0 — USER’ S MANUAL 397