In the various Concert Technology APIs, you have a choice of three implementations of FeasOpt, specifying that you want to allow changes to the bounds on variables, to the ranges on constraints, or to both.

In the Callable Library, you can allow changes without distinguishing bounds on variables from ranges over constraints.

In each of the APIs, there is an additional argument where you specify whether you want merely a feasible solution suggested by the bounds and ranges that FeasOpt identifies, or an optimized solution that uses these bounds and ranges.