Re: Help with compareTo()

[JacobFeldman]

Wee,

You cannot use Java's method "compareTo" directly but rather you should post the implies-constraints as below:

public static void main(String[] args) {

Problem p = ProblemFactory.newProblem("TestCompareTo");

        Var x = p.variable("X", 0, 3);

        Var y = p.variable("Y", 0, 3);

        Var cost = p.variable("Cost", 0, 10);

        Constraint more = p.linear(x, ">", y);

        Constraint lessOrEqual = p.linear(x, "<=", y);

        Constraint minus = p.linear(cost, "=", x.minus(y));

        Constraint plus = p.linear(cost, "=", x.plus(y));

        more.implies(minus).post();

        lessOrEqual.implies(plus).post();

        

        p.log("=== Find solution");

        Solver solver = p.getSolver();

        Solution solution = solver.findOptimalSolution(Objective.MAXIMIZE, cost);

        solution.log();

}

This code produces:

=== Find solution

Solution #1:

X[3] Y[3] Cost[6]

Of course, you may use all possible comparisons of constrained variables x and y.

On Monday, April 29, 2013 6:25:04 AM UTC-4, wee...@gmail.com wrote:

Dear all,

I am trying to write a simple example as follows:

-----------------------------------------------------------------------------------------------------
        Problem p = ProblemFactory.newProblem("SimpleTest");
        Var x = p.variable("X", 0, 3);
        Var y = p.variable("Y", 0, 3);
        Var cost = p.variable("C", 0, 10);
       
        if (x.compareTo(y) == 1) {
            cost = x.minus(y);
        } else {
            cost = x.plus(y);
        }
       
        p.log("=== Find solution");
        Solver solver = p.getSolver();
        Solution solution = solver.findOptimalSolution(Objective.MAXIMIZE, cost);
------------------------------------------------------------------------------------------------------------------------

As you can see, the value of the variable "cost" is dependent on the other two variables "x" and "y".
The objective is to find a solution that maximizes the value of "cost".

The results from running this example is:
=== Find solution
Solution #1:
     X[3] Y[0] C[0] [3]

Can anyone tell me whether I am using the function compareTo() properly?
I thought the optimal solution would either be X[2] Y[3], or X[3] Y[2].
In addition, why is the value of "C" shown as 0 in the results, while the value of "cost" is shown as 3?

Thank you in advance for your help.

Wee Lum