Final Iteration Convergence Bound of Q-Learning: Switching System Approach

TL;DR

This paper establishes a finite-time convergence bound for the final iterate of Q-learning using a switching system approach, addressing limitations of prior averaged-iterate bounds and offering new insights into RL algorithm analysis.

Contribution

It introduces a finite-time error bound for the final iterate of Q-learning based on a switching system framework, expanding analysis beyond averaged iterates.

Findings

Finite-time error bound for Q-learning's final iterate.

Analysis covers different scenarios compared to previous work.

Provides insights connecting Q-learning with discrete-time switching systems.

Abstract

Q-learning is known as one of the fundamental reinforcement learning (RL) algorithms. Its convergence has been the focus of extensive research over the past several decades. Recently, a new finitetime error bound and analysis for Q-learning was introduced using a switching system framework. This approach views the dynamics of Q-learning as a discrete-time stochastic switching system. The prior study established a finite-time error bound on the averaged iterates using Lyapunov functions, offering further insights into Q-learning. While valuable, the analysis focuses on error bounds of the averaged iterate, which comes with the inherent disadvantages: it necessitates extra averaging steps, which can decelerate the convergence rate. Moreover, the final iterate, being the original format of Q-learning, is more commonly used and is often regarded as a more intuitive and natural form in the majority of iterative algorithms. In this paper, we present a finite-time error bound on the final iterate of Q-learning based on the switching system framework. The proposed error bounds have different features compared to the previous works, and cover different scenarios. Finally, we expect that the proposed results provide additional insights on Q-learning via connections with discrete-time switching systems, and can potentially present a new template for finite-time analysis of more general RL algorithms.