CPLEX java - Equality constraints for multidimensional arrays

Question

I am solving a Linear Programming using CPLEX in Java. I have a binary decision variable defined as

IloNumVar[] xd = new IloNumVar[Tend];

where Tend is the time. The decision variable is subject to the constraint that the sum over time of xd must be equal a given integer C_d, which was implemented as:

cplex.addEq(cplex.sum(xd), C_d);

So far everything was working.

The problem I am having is that now I am trying to generalize the number of decision variables using a multidimensional array:

IloNumVar[][] xd = new IloNumVar[Tend][count_d];

but I still need to impose the constraint that the sum of each decision variable over time must be equal to a constant. I tried with this:

IloNumVar[] Sum_d   = new IloNumVar[Tend];
IloNumVar[]  Sum_D  = new IloNumVar[1];
for(int j=0;j<count_d;j++){
    for (int i = 1; i<Tend; i++){
        cplex.addEq(Sum_d[i],cplex.sum(Sum_d[i-1],xd[i][j])); 
        }
    cplex.addEq(Sum_d[Tend],Sum_D);
    cplex.addEq(Sum_D,C_d);
    }

but I get the following errors: Multiple markers at this line

The method addEq(IloNumExpr, double) in the type IloCplexModeler is not applicable for the arguments (IloNumVar, IloNumVar[])
The method addEq(IloNumExpr, double) in the type IloCplexModeler is not applicable for the arguments (IloNumVar[], int)

I am not quite sure what is the proper way to include the equivalent constraint in the problem definition.

Any suggestion would be much appreciated.

Jacko Jacko · Accepted Answer · 2016-06-11T15:35:34

The error is due to non-respect of the addEq overloads.

In all of the six overloads of the addEq function the RHS of the equation you're adding to your model is to be an integer. Its always a double or another IloNumExpr.

Therefore, you only need to declare:

double C_d

One is glad to be of service!

CPLEX java - Equality constraints for multidimensional arrays

1 Answers