How to define a function in Z3 java API?

Question

I am learning to run the similar codes in the matching case, which is for matching the trucks for transportation( https://www.microsoft.com/en-us/research/wp-content/uploads/2016/02/nbjorner-nuz.pdf ) in JAVA API. There is a code for defining the max function:

(define-fun imax ((a Int) (b Int)) Int (if (> a b) a b))

I translate that to Java:

     public static ArithExpr maxFunc(ArithExpr a, ArithExpr b)
     {
         Context ctx = new Context();
         ArithExpr result = (ArithExpr) ctx.mkITE(ctx.mkGe(a, b), a, b);
         return result;
     }

And try to use it in the same way(the following is just a demo)

        ArithExpr per1 = maxFunc(X0101, maxFunc(X0201, maxFunc(X0301, maxFunc(X0401, X0501))));
        BoolExpr minPer1 = ctx.mkEq(per1, constant0);
        o.AssertSoft(minPer1,1 , "a");

There are errors for the above codes:

Exception in thread "main" com.microsoft.z3.Z3Exception: Context mismatch

The error refers to the function body:

ArithExpr result = (ArithExpr) ctx.mkITE(ctx.mkGe(a, b), a, b);

I definitely have doubts in constructing the z3 function in JAVA. Does there exist special function form for Z3 Java API? How to fix the function?

Answer 1

"Context mismatch" means that you're trying to use expressions from multiple contexts together, which is not supported. Instead of Context ctx = new Context(); , make sure you use the same context that you use in the rest of your program.