We establish two concentration inequalities for nonlinear stochastic system under time-varying contraction conditions. The key to our approach is an energy function termed Averaged Moment Generating Function (AMGF). By combining it with incremental stability analysis, we develop a concentration inequality that bounds the deviation between the stochastic system state and its deterministic counterpart. As this inequality is restricted to single time instance, we further combine AMGF with martingale-based methods to derive a concentration inequality that bounds the fluctuation of the entire stochastic trajectory. Additionally, by synthesizing the two results, we significantly improve the trajectory-level concentration inequality for strongly contractive systems. Given the probability level $1-δ$, the derived inequalities ensure an $\mO(\sqrt{\log(1/δ))}$ bound on the deviation of stochastic trajectories, which is tight under our assumptions. Our results are exemplified through a case study on stochastic safe control.
Contraction Theory for Nonlinear Stability Analysis and Learning-based Control: A Tutorial Overview
Division of Engineering and Applied Science, California Institute of Technology, Pasadena, CA, USA（加州理工学院工程与应用科学系）；Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA（加州理工学院喷气推进实验室）；Nonlinear Systems Laboratory, Massachusetts Institute of Technology, Cambridge MA, USA（麻省理工学院非线性系统实验室）
Finite-Time Concentration and Convergence Rates for Projected Two-Time-Scale Stochastic Approximation with Markov Noise
Laboratoire de Recherche de l’EPITA（EPITA研究实验室）；Indian Institute of Technology Bombay（印度理工学院孟买分校）；Mohamed bin Zayed University of Artificial Intelligence（穆罕默德·本·扎耶德人工智能大学）
