Cplex Java for solving a small model

Question

I am trying to solve a problem similar to the TSP with additional constraint (weight), I already wrote my code in Java, but I have a problem when compiling : This is my code :

  package example01;
  import ilog.concert.*;
  import ilog.cplex.*;
  import java.io.*;
  import java.util.Arrays;

  public class modele {
  public static void solveme1 (){

        int     n    = 5;           
        int     [] W = {1,2,3,4,5};         
        int      [][]   distance =  {
                 {  0,14,10,12,20 },
                 {  14,0,23,4,30 },
                 {  10,23,0,25,18 },
                 {  12,4,25,0,17 },
                 {  20,30,18,17,0 },
             };

        try {
            IloCplex cplex = new IloCplex();

            //variables
            IloNumVar[][] x = new IloNumVar[n][];
            for (int i=0; i<n ; i++){
                x[i] = cplex.boolVarArray(n);
            }

            IloNumVar [] time = cplex.numVarArray(n, 0, Double.MAX_VALUE);

            // objective
            IloLinearNumExpr obj = cplex.linearNumExpr();
            for (int i =0; i<n; i++) {                  
                        obj.addTerm(time[i], W[i]);

            }
            cplex.addMinimize(obj);             

            //constraints
            // Flux In
            for (int j=0; j<n; j++){
                IloLinearNumExpr expr = cplex.linearNumExpr();
                for(int i=0; i<n; i++){
                    if (i!=j){
                        expr.addTerm(1.0,x[i][j]);
                    }
                }
                cplex.addEq(expr, 1);               
            }

            // Flux Out
            for (int j=0; j<n; j++){
                IloLinearNumExpr expr = cplex.linearNumExpr();
                for(int i=0; i<n; i++){
                    if (i!=j){
                        expr.addTerm(1.0,x[j][i]);
                    }
                }
                cplex.addEq(expr, 1);                   
            }
            // Starting at time =0
            cplex.addEq(time[0],0);

            // To force the starting from the location 0
            for (int j=1; j<n; j++){
                IloLinearNumExpr expr = cplex.linearNumExpr();
                expr.addTerm(1.0,x[0][j]);
                cplex.addEq(expr, 1);
            }

            // Constraint to determine the time in "J" after visiting "I"
            for (int j=0; j<n;j++){
                for (int i=0;i<n;i++){
                        if (i!=j){
                        cplex.addGe(time[j],  cplex.sum(cplex.sum(time[i], cplex.prod(x[i][j], 
                        distance[i][j])),cplex.prod(cplex.sum(x[i][j],-1),Double.MAX_VALUE)));
                        }
                }
            }

    if (cplex.solve()) 
    {
    System.out.println("objective = "+cplex.getObjValue());
    }
    else {
    System.out.println("Not solved");

    }
    cplex.end();

 }
        catch (IloException e){
            e.printStackTrace();
        }
    }
 }

The journal Log is as following :

"Column 'x2' set to infinite lower bound. Presolve time = 0.00 sec. (0.01 ticks) Root node processing (before b&c): Real time = 0.00 sec. (0.01 ticks) Parallel b&c, 8 threads: Real time = 0.00 sec. (0.00 ticks) Sync time (average) = 0.00 sec. Wait time (average) = 0.00 sec.
Total (root+branch&cut) = 0.00 sec. (0.01 ticks) Not solved"

Thank you in advance for your answers ! */

Answer 1

You state you have a problem when compiling. It seems to me you get a problem when running the program, and it's cplex telling you that the model is infeasible (a variable with an infinite lower bound doesn't sound feasible).