Implementation of a parametrized objective function without using module variables or internal subroutines

[zaikunzhang]

@jwmwalrus

Your second case is invalid due to interface mismatch —i.e., you are providing a procedure with three arguments to the solver, which expects a procedure with two arguments.

Even though it is valid to call problem%objective(x, y), the interface of problem%objective does not comply with OBJ(x, y). This felt a bit inconsistent to me.