Originally posted by: gorlami

I am trying to code the expression a = b = c as a constraint in C# Cplex.

Currently, I have tried splitting the expression into two, and using the AddEq function for both.

My code thus far is as follows:

 INumExpr constraint21 = model.NumExpr();
            INumExpr constraint22 = model.NumExpr();
            for (int k = 0; k < numberOfTrucks; k++)
            {
                for (int j = 0; j < numberOfNodes; j++)
                {
                    constraint21 = model.Sum(constraint21, route[0, j, k]);
                    constraint22 = model.Sum(constraint22, route[j, 0, k]);
                }
            }
            model.AddEq(numberOfTrucks, constraint21);
            model.AddEq(numberOfTrucks, constraint22);

I need constraint21 = constraint22 = numberOfTrucks to be fulfilled.

This way of expressing the constraint seems problematic. Is there maybe another function that can handle the equation a=b=c directly without splitting?

Thank you

No, there is no way to add a constraint that forces 3 expressions to be equal. This has to be modeled by 2 equations.

What are the problems you are observing with this formulation?

Note that you can use an ILinearNumExpr to write code that is more efficient:

ILinearNumExpr constraint21 = model.LinearNumExpr();
...
    constraint21.AddTerm(1.0, route[0, k, k]);