Characterizing Lookahead Dynamics of Smooth Games
Authors: Junsoo Ha, Gunhee Kim
Keywords: Lookahead optimizer, game dynamics, smooth game
Abstract: As multi-agent systems proliferate in machine learning research, games have attracted much attention as a framework to understand optimization of multiple interacting objectives. However, a key challenge in game optimization is that, in general, there is no guarantee for usual gradient-based methods to converge to a local solution of the game. The latest work by Chavdarova et al. (2020) report that Lookahead optimizer (Zhang et al. (2019)) significantly improves the performance of Generative Adversarial Networks (GANs) and reduces the rotational force of bilinear games. While promising, their observations were purely empirical, and Lookahead optimization of smooth games still lacks theoretical understanding. In this paper, we fill this gap by theoretically characterizing Lookahead dynamics of smooth games. We provide an intuitive geometric explanation on how and when Lookahead can improve game dynamics in terms of stability and convergence. Furthermore, we present sufficient conditions under which Lookahead optimization of bilinear games provably stabilizes or accelerates convergence to a Nash equilibrium of the game. Finally, we show that Lookahead optimizer preserves locally asymptotically stable equilibria of base dynamics and can either stabilize or accelerate the local convergence to a given equilibrium with proper assumptions. We verify each of our theoretical predictions by conducting numerical experiments on two-player zero-sum (non-linear) games.