Originally posted by: SystemAdmin

I write some code to model an optimization problem:

//create two dimensions NxN array
IloIntArray2Dimensions y(env);
                for(int i=0;i<nbNodes;i++)
                {
                        y.add(IloIntVarArray(env,nbNodes));
                }
 
//assign name to variables
IloIntArray2Dimensions y(env);
                for(int i=0;i<nbNodes;i++)
                {
                        y.add(IloIntVarArray(env,nbNodes));
                }
 
                for(int i=0;i<nbNodes;i++)
                        for(int j=0;j<nbNodes;j++)
                        {
                                y[i][j]=IloIntVar(env,0,1);
                                sprintf(name,"y_%d.%d",i,j);
                                y[i][j].setName(name);
                        }
 
                //define objective function
                IloExpr exprobjective(env);
                for(int i=0;i<nbNodes;i++)
                        for(int j=0;j<nbNodes;j++)
                                if (capacity[i][j] > 0)
                                {
                                        exprobjective+=fixedcost[i][j]*y[i][j];  
                                }
//add objective function
                model.add(IloMinimize(env,exprobjective));
                exprobjective.end();

and I export the model to a .lp file:

---

\Problem name: IloCplex

Minimize
obj: 3173 y_0.3 + ... + 5242 y_9.7 + id103
Bounds
0 <= y_0.3 <= 1
....
0 <= y_9.7 <= 1
id103 = 0
Binaries
y_0.3 ... y_9.7
End

---

My problem is that : I do not know where the constraint (variable) id103 = 0 comes from. I only have some integer variables; an objective function and I already assigned a name to these integer variables. If I remove the objective function, nothing appears in .lp file.

Thanks for your suggestion.
#CPLEXOptimizers
#DecisionOptimization

Originally posted by: SystemAdmin

Sorry for the mistake during the copy/paste, the first 4 line of the source code is repeated.
#CPLEXOptimizers
#DecisionOptimization

Originally posted by: SystemAdmin

If I uncomment other constraints and comment objective expression, the unknown variable disappeared, so this problem relates to the objective function. But I have not understood why.

Thanks for your comments,

Lessi.
#CPLEXOptimizers
#DecisionOptimization

Originally posted by: SystemAdmin

id103 (CPLEX's internal name) is a continuous variable that represents the constant term of your objective function. The model constrains it to be zero. Had you specified a nonzero value for the constant in the objective function, id103 would have been constrained to that value. It is nothing to worry about.

/Paul

Mathematicians are like Frenchmen: whenever you say something to them, they translate it into their own language, and at once it is something entirely different. (Goethe)
#CPLEXOptimizers
#DecisionOptimization

Originally posted by: SystemAdmin

Thanks for your explanation, It is clear to me now.

Lessi.
#CPLEXOptimizers
#DecisionOptimization