Nonlinear H-infinity state feedback controllers: Computation of valid region

''From a general point of view the state feedback H-infinity suboptimal control problem is reasonable well-understood. Important problems remain with regard to a priori information of the size of the neighbourhood where the local state feedback H-infinity problem is solvable, and with regard to the nature of solutions V to the Hamilton-Jacabi inequalities ... such as properness of V as a candidate Lyapunov function'' Citation van der Schaft, 1992 [vdS92]. The first of these problems is solved regionally (semi-globally) in this paper, and the obtained control laws are implemented in MAPLE.