Cplex Java add expr(sum) to objective function

Question

I've got the following objective function:

minimize sum (trueck[k] - time[k]) for all k (1..n).

I tried to set it up like this:

IloLinearNumExpr obj = cplex.linearNumExpr();

for(int k=0; k<grossK.length; k++){
    obj.addTerm(1.0, cplex.sum(trueck[k], cplex.negative(time[k])));
}

cplex.addMinimize(obj);

The eclipse error message for the 4th line is:

"The method addTerm(double, IloNumVar) in the type IloLinearNumExpr is not applicable for the arguments (double, IloNumExpr)"

I guess the method "addTerm" is wrong but I can't find a solution. Thanks in advance.

Ram Narasimhan Ram Narasimhan · Accepted Answer · 2013-07-31T18:29:42

Don't use cplex.sum inside addTerm. You just need to separate out the two terms in your Objective function, since they both are summed over k.

Minimize sum (trueck[k] - time[k]) for all k (1..n)

Is the same as Min *sum_over_k* (trueck[k]) - *sum_over_k* (time[k])

This way, addTerm can handle it. (The code below is untested, but it gives you the idea of what you should try.)

IloLinearNumExpr obj = cplex.linearNumExpr();

for(int k=0; k<grossK.length; k++){
    obj.addTerm(1.0, trueck[k]);
    obj.addTerm(-1.0, time[k]);
}

cplex.addMinimize(obj);

Hope that helps.

Cplex Java add expr(sum) to objective function

2 Answers