Sets the relative tolerance for objective function f(x).
Equivalent in C API: nlopt_set_ftol_rel
Params: tol = value of tolerance, default determined by enum defaultTol
auto opt = Opt(Algorithm.auglag, 2); opt.setFTolRel(1e-4); assert(opt.getResult() > 0);
See Implementation
Sets the relative tolerance for objective function f(x).
Equivalent in C API: nlopt_set_ftol_rel