Hello,

I am trying to use CPLEX to build a transportation network, where arcs  are open so that commodities can be delivered on trucks from origin to destination with different start and end periods.

I am getting a number of the same error with my code (constraints 2 and 4, the error is of the same nature for both constraints): OPL cannot extract expression. I am not sure how to fix this, I can only assume that OPL does not support my expressions of constraint. I would be very grateful for any help or advice, how I could make my constraints not so complex.

I have attached the model, the data and an excel files that are needed to read in the data.

I am only a beginner so I apologize for any mistakes. Please help.

//ct2  
 forall (i in tnodes, v in Vehicle)    //number of incoming&outgoing arcs for each node is equal
       ct2:sum (a in Nplus[i]:a in arcs) y[v][a]==sum (a in Nminus[i]:a in arcs) y[v][a];​

//ct4  
forall(d in demand,i in tnodes){
  ct4:if(i == d.Origin )sum(a in Nplus[i]:a in arcs)x[d][a] - sum(a in Nminus[i]:a in arcs)x[d][a]==dem[d];
    else if (i == d.Destination )sum(a in Nplus[i]:a in arcs)x[d][a] - sum(a in Nminus[i]:a in arcs)x[d][a]==-dem[d];
      else sum(a in Nplus[i]:a in arcs)x[d][a] - sum(a in Nminus[i]:a in arcs)x[d][a]==0;

forall (i in tnodes, v in Vehicle)    //number of incoming&outgoing arcs for each node is equal
  ct2:sum (a in Nplus[i]) y[v][a]==sum (<f,t> in Nminus[i]) y[v][<t,f>];​

//ct2   forall (i in tnodes, v in Vehicle)    //number of incoming&outgoing arcs for each node is equal       ct2:sum (a in Nplus[i]:a in arcs) y[v][a]==sum (a in Nminus[i]:a in arcs) y[v][a];​

//ct4  forall(d in demand,i in tnodes){  ct4:if(i == d.Origin )sum(a in Nplus[i]:a in arcs)x[d][a] - sum(a in Nminus[i]:a in arcs)x[d][a]==dem[d];    else if (i == d.Destination )sum(a in Nplus[i]:a in arcs)x[d][a] - sum(a in Nminus[i]:a in arcs)x[d][a]==-dem[d];      else sum(a in Nplus[i]:a in arcs)x[d][a] - sum(a in Nminus[i]:a in arcs)x[d][a]==0;