Originally posted by: JuanCarlosPego

Hi, I'm trying to model the OPL CrewScheduling example within CP OPTIMIZER. The calculation of the solution works pretty fast for 100 but when I try to throw for more than 100 hangs. The last test flights realized for 1500 and I had to kill the process after 24 hours of calculation. Specifically cvrpair.mod file. The constraint that makes you go slow is number 6.

    IloInt nSeq    = 10;
    IloInt maxTime = 600;    // maximum time between the nSeq flights
    IloInt nbFlight=100;  // Flights

    IloIntVarArray vloMembers(env, nSeq, 0, nbFlight);    

    // Constraint 1
    // El vuelo X tiene que estar en el pair
        model.add(IloCount(vloMembers, IdVlo) == 1);

    // Constraint 2        
    // El pair tiene que comenzar en la base X
        model.add(citySeq[vloMembers[0]] == IdBase);

    // Constraint 3    
    // el origen del pair tiene que ser igual al final
         model.add(citySeq[vloMembers[0]] == citySeq[vloMembers[nSeq-1]]);
        
    // Constraint 4                
        for (IloInt i = 1; i < nSeq; i++){
             model.add(Arr[vloMembers[i-1]]+minStop<Dep[vloMembers[i]] || (Arr[vloMembers[i-1]]+minStop>=Dep[vloMembers[i]] && Arr[vloMembers[i]]==0));
             model.add(citySeq[vloMembers[i-1]]==citySeq[vloMembers[i]]);
        }        

    // Constraint 5                
        for(IloInt i = 1; i < nSeq; i++){
            for(IloInt j = i+1; j < nSeq; j++){
                model.add(IloIfThen(env,(citySeq[vloMembers[i-1]]==citySeq[vloMembers[i]]),(citySeq[vloMembers[j-1]]==citySeq[vloMembers[j]])));
            }
         }        
        
    // Constraint 6        ** very very slow  ***        
        IloIntExpr Sum_time(env);
         for (i = 0; i < nSeq; i++){
             Sum_time=Sum_time+(Arr[vloMembers[i]]-Dep[vloMembers[i]]);
         }
         model.add(Sum_time<maxTime);
        Sum_time.end();
        
        
         // order the vloMembers to break symmetry
        for (i = 0; i < nSeq-1; i++)    model.add(vloMembers[i] <= vloMembers[i+1]);
        
        IloCP cp(model);
        cp.setParameter(IloCP::LogVerbosity, IloCP::Quiet);
        cp.setParameter(IloCP::SearchType, IloCP::DepthFirst);
        cp.setParameter(IloCP::Workers, 1);
        cp.startNewSearch();
        int contador=0;
        while (cp.next() && contador<10) {
            for (i = 0; i < nSeq; i++){
                tuple[i] = cp.getValue(vloMembers[i]);
                ....
            
            contador++;            
        }
        ...

thank you very much.

Juan Carlos

Originally posted by: ol

Hello,

I see:

    cp.setParameter(IloCP::SearchType, IloCP::DepthFirst);

Did you try without this line? Depth first search is not a good approach for large search space, which seems to be your case. Removing this line will allow CP Optimizer to launch a much more powerful search method.

Regards,

Olivier