Originally posted by: A.Omidi

Dear community team,

I'm trying to debug an optimization model using CPLEX. I created a MPS file. While I'm using CPLEX_CMD optimizer, it works fine but, in the Java API, I have some issues. In the CPLEX user manual, it has been mentioned we need to build a specific method to invoke the conflict refiner (IloCplex.refineConflict).

I'm wondering if:

1- Is there any example to use conflict refiner using Java API?

2- Should I use a method such as callback to invoke the conflict refiner? if so, is there any Javadoc?

Regards

Abbas

Hi Abbas,

Here is an example of using the conflict refiner using the Java API:

import java.io.BufferedReader;
import java.io.FileReader;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import ilog.concert.*;
import ilog.cplex.*;


/**
 * Read a problem and use the conflict refiner.
 *
 * See the usage message below for more details.
 */
public class ConflictEx1 {

   /**
    * Display a usage message and exit.
    */
   static void usage() {
      System.out.println("Usage: java ConflictEx1 filename");
      System.out.println("  filename   Name of a file, with .mps, .lp, or .sav");
      System.out.println("             extension, and a possible, additional .gz");
      System.out.println("             extension");
      System.exit(2);
   }

   /**
    * Invoke the conflict refiner on a model and display the results.
    */
   public static void main(String[] args) throws Exception {
      if (args.length != 1) {
         usage();
      }

      // Create the modeler/solver object
      try (IloCplex cplex = new IloCplex()) {
         // Read model from file with name args[0] into cplex optimizer object.
         cplex.importModel(args[0]);

         // Access the IloLPMatrix object that has been read from a file in
         // order to access variables which are the columns of the LP.  The
         // method importModel() guarantees that exactly one IloLPMatrix
         // object will exist, which is why no tests or iterators are
         // needed in the following line of code.
         IloLPMatrix lp = (IloLPMatrix)cplex.LPMatrixIterator().next();

         IloRange[] rng = lp.getRanges();

         // Calculate the number of non-boolean variables.
         final int numVars = cplex.getNcols() - cplex.getNbinVars();

         // Find the number of SOSs in the model.
         final int numSOS = cplex.getNSOSs();

         // Gather array of constraints to be considered by the conflict
         // refiner.
         List<IloConstraint> constraints = new ArrayList<IloConstraint>();
         for (int i = 0; i < rng.length; ++i) {
            constraints.add(rng[i]);
         }

         // Add variable bounds to the constraints array.
         for (IloNumVar v : lp.getNumVars()) {
            if (v.getType() != IloNumVarType.Bool) {
               constraints.add(cplex.lowerBound(v));
               constraints.add(cplex.upperBound(v));
            }
         }

         // Add SOSs to the constraints array.
         if (numSOS > 0) {
            Iterator s1 = cplex.SOS1iterator();
            while (s1.hasNext()) {
               IloSOS1 cur = (IloSOS1)s1.next();
               constraints.add(cur);
            }
            Iterator s2 = cplex.SOS2iterator();
            while (s2.hasNext()) {
               IloSOS2 cur = (IloSOS2)s2.next();
               constraints.add(cur);
            }
         }

         // Define preferences for the constraints. Here, we give all
         // constraints a preference of 1.0, so they will be treated
         // equally.
         double[] prefs = new double[constraints.size()];
         for (int i = 0; i < prefs.length; ++i) {
            prefs[i] = 1.0;
         }

         IloConstraint[] cons = constraints.toArray(
            new IloConstraint[constraints.size()]);

         // Run the conflict refiner. As opposed to letting the conflict
         // refiner run to completion (as is done here), the user can set
         // a resource limit (e.g., a time limit, an iteration limit, or
         // node limit) and still potentially get a "possible" conflict.
         if (cplex.refineConflict(cons, prefs)) {
            // Display the solution status.
            System.out.println("Solution status = " + cplex.getCplexStatus());

            // Get the conflict status for the constraints that were specified.
            IloCplex.ConflictStatus[] conflict = cplex.getConflict(cons);

            // Count the number of conflicts found for each constraint group and
            // print the results.
            int numConConflicts = 0;
            int numBoundConflicts = 0;
            int numSOSConflicts = 0;
            for (int i = 0; i < cons.length; ++i) {
               IloConstraint c = cons[i];
               if (conflict[i] == IloCplex.ConflictStatus.Member ||
                   conflict[i] == IloCplex.ConflictStatus.PossibleMember) {
                  if (c instanceof IloRange)
                     numConConflicts++;
                  else if (c instanceof IloNumVarBound)
                     numBoundConflicts++;
                  else
                     numSOSConflicts++;
               }
            }

            // Display a conflict summary.
            System.out.println("Conflict Summary:");
            System.out.println("  Constraint conflicts     = " + numConConflicts);
            System.out.println("  Variable Bound conflicts = " + numBoundConflicts);
            System.out.println("  SOS conflicts            = " + numSOSConflicts);

            // Write the identified conflict in the LP format.
            final String confFile = "ConflictEx1.java.lp";
            System.out.printf("Writing conflict file to '%s'....%n", confFile);
            cplex.writeConflict(confFile);

            // Display the entire conflict subproblem.
            try (BufferedReader br = new BufferedReader(new FileReader(confFile))) {
               String line = null;
               while ((line = br.readLine()) != null) {
                  System.out.println(line);
               }
            }
         }
         else {
            System.out.println("A conflict was not identified.");
            System.out.println("Exiting....");
            return;
         }
      }
   }
}

No callbacks are required. I posted a small example years ago, but it should still work: Turning Bounds into Constraints in CPLEX.

Originally posted by: A.Omidi

Dear Prof. Rubin and RyanKersh,

Many thanks for the detailed explanations.

Regards

Abbas