Originally posted by: HuiD

Hi, I'm trying to write one of the constraints, one decision variable decide another decision variable.

dvar boolean x[u in RV][v in RV][t in dem];
dvar int z[u in RV][t in dem] in 1..N;
 
subject to {
        forall(t in dem, u in RV) {
                forall(v in OL[u]) {
                        if(x[u][v][t] == 1)
                                z[t][u] == z[t][v] + 1;
                }
        }
}

there will be an error "decision variable ’x' is node allowed."

How can I write these constraints properly? The variable z cannot be compute by the input matrix, but decide by the decision variable x.

Thanks
#DecisionOptimization
#OPLusingCPLEXOptimizer

Originally posted by: SystemAdmin

Hi,

you should use conditinal constraints, i.e. something like

//... as in your formulation
   (x[u][v][t] == 1) =>(z[t][u] == z[t][v] + 1);

Best regards
Norbert
#DecisionOptimization
#OPLusingCPLEXOptimizer

Originally posted by: HuiD

Thanks, Norbert, your code is right.

I cannot find the conditional constraints writing like this in the OPL manual, is there other references?

Hui
#DecisionOptimization
#OPLusingCPLEXOptimizer

Originally posted by: SystemAdmin

Sorry, gave you the wrong keyword. It should have been "logical constraints".

Please have a look at:

IDE and OPL > Optimization Programming Language (OPL) >
Language User’s Manual >
The application areas >
Tutorial: Using CPLEX logical constraints

Regards
Norbert
#DecisionOptimization
#OPLusingCPLEXOptimizer

Originally posted by: HuiD

Oh, I can find it now, thanks!

Hui
#DecisionOptimization
#OPLusingCPLEXOptimizer