OPL Script – Accessing variable indexed by tuple

Hi there,

I am new to this forum, so I apologize if I make any mistake. I have searched for similar problems but have not managed to find a solution.

I have a model in which a decision variable is indexed by a tuple set, which I define in a .mod file:

//Define tuple
tuple fvts {
 string F;
 string V;
 int T;
 string S; 
 }

//Declare tuple set
{fvts} fvts_ = ...;

//Declare decision variable
dvar int+ sh[ in fvts_];

In a separate .mod file, I have a flow control script in which I iteratively changes the upper bounds of N of these variables to 1. To select which variables are updated, a sub-problem (defined in yet another .mod file) is solved, and the decision variables are ranked according to a user-defined function which compares the results of the main model and the sub-model. To do so, I’m using the following script:

main {
    ...

    //main_model is the main model, m3 is the sub-model

    // Generate array of tuples from tuple set
    var list = new Array();
    var j = 1;
    for (var i in main_model.fvts_) {
      list[j] = i;
      j++;
    }
    
    // Order array of tuples according to the value a user-defined function
    list.sort(compareFactor);
    
    //Update the upper-bound of the top N variables
    for (var l = 1; l <= N; l++) {
      var s = main_model.fvts_.find(list[l]);
      main_model.sh[s].UB = 1; 
    }
    
  ...

}

The list is successfully ordered as expected. However, the problem is that at the second iteration of the second loop, I get the error "OPL cannot extract expression: sh#231.". I have isolated this error to the "main_model.sh[s].UB" part, since the "main_model.fvts_.find(list[l])" behaves as expected. However, I know that the decision-variable with that tuple as index exists, and I am not able to access it.

Any ideas on what may causing this error and how to fix it?

Thanks in advance for any help!

Cheers,

Guilherme