Originally posted by: brown_rice

Hi,

I am trying to add a term [alpha*(1- x -y) ] into linear expression, but I receive an error. What could I be doing wrong? or is there a better way to state this? 

IloLinearNumExpr expr = cplex.linearNumExpr();

expr.addTerm(myArray[i], cplex.diff(1, cplex.sum(firstVar[i],secVar[i])));

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

You just need an explicit cast of the second argument:

expr.addTerm(myArray[i], (IloLinearNumExpr) cplex.diff(1, cplex.sum(firstVar[i],secVar[i])));

Because sum() and diff() can be applied to certain nonlinear expressions (such as quadratics), their argument and return types are the more general IloNumExpr. The addTerm() method needs a linear expression. Your expression is linear, so you just need to cast it as such.

Originally posted by: brown_rice

Thanks for the clear explanation but I still receive the same error.

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

I also tried; 

expr.addTerm(myArray[i], (IloLinearNumExpr) cplex.diff(1, (IloLinearNumExpr) cplex.sum(firstVar[i],secVar[i])));

but did not work. Just for now, I am going with

expr.setConstant(Arrays.stream(myArray).sum());
for(){
    expr.addTerm(-myArray[i],firstVar[i]);
    expr.addTerm(-myArray[i],secVar[i]);
}

and it works.

Sorry, I missed a couple of things in your original question. First, I saw "addTerm()" but thought "add()". As the name implies, "addTerm()" wants a single term, whereas "add()" takes as its argument an expression. The more subtle thing I missed is that you cannot cast sum() or diff() to IloLinearNumExpr. I'm not sure why not, and I thought I had done so in the past, but apparently not.

Originally posted by: brown_rice

In the original question, I was still using addTerm in a for loop, but just did not show that (for some reason, I thought it'd be redundant). The important part is that I did not know this "you cannot cast sum() or diff() to IloLinearNumExpr". I guess, defining the function component by component is the way to go in this case. Thanks for the help.