Minimum restraint functions for unbounded dynamics: general and control-polynomial systems

We consider an exit-time minimum problem with a nonnegative running cost and unbounded controls. The occurrence of points where the cost is zero can be regarded as a transversality loss. Furthermore, since controls range over unbounded sets, the family of admissible trajectories may lack important compactness properties. In the first part of the paper we show that the existence of a p--Minimum Restraint Function provides not only global asymptotic controllability (despite non-transversality) but also a state-dependent upper bound for the value function. This extends to unbounded dynamics a former result which heavily relied on the compactness of the control set. In the second part of the paper we apply the general result to the case when the system is polynomial in the control variable. Some elementary, algebraic, properties of the convex hull of vector-valued polynomials' ranges allow some simplifications of the main result, in terms of either near-affine-control systems or reduction to weak subsystems for the original dynamics.