A Lie-bracket-based notion of stabilizing feedback in optimal control

TL;DR

This paper explores a Lie-bracket-based framework for stabilizing feedback in optimal control, linking stabilizability, controllability, and cost regulation through the concept of Minimum Restraint Functions.

Contribution

It introduces a novel Lie-bracket-based notion of stabilizing feedback that incorporates iterated Lie brackets for cost regulation in control systems.

Findings

Asymptotic controllability is necessary for degree-k stabilizability.

The framework connects stabilizability with the existence of Minimum Restraint Functions.

Main results establish the link between stabilizability and controllability with cost regulation.

Abstract

For a control system two major issues can be considered: the stabilizability with respect to a given target, and the minimization of an integral functional (while the trajectories reach this target). Here we consider a problem where stabilizability or controllability are investigated together with the further aim of a "cost regulation", namely a state-dependent upper bounding of the functional. This paper is devoted to a crucial step in the program of establishing a chain of equivalences among degree-k stabilizability with regulated cost, asymptotic controllability with regulated cost, and the existence of a degree-k Minimum Restraint Function (which is a special kind of Control Lyapunov Function). Besides the presence of a cost we allow the stabilizing "feedback" to give rise to directions that range in the union of original directions and the family of iterated Lie bracket of length less or equal to $k$. In the main result asymptotic controllability [resp. with regulated cost] is proved to be necessary for degree-k stabilizability [resp. with regulated cost]. Further steps of the above-mentioned logical chain are proved in companion papers, so that also a Lyapunov-type inverse theorem -- i.e. the possibility of deriving existence of a Minimum Restraint Function from stabilizability -- appears as quite likely.