We show for the first time, to our knowledge, that it is possible to reconcile in online learning in zero-sum games two seemingly contradictory objectives: vanishing time-average regret and non-vanishing step sizes. This phenomenon, that we coin ``fast and furious" learning in games, sets a new benchmark about what is possible both in max-min optimization as well as in multi-agent systems. Our analysis does not depend on introducing a carefully tailored dynamic. Instead we focus on the most well studied online dynamic, gradient descent. Similarly, we focus on the simplest textbook class of games, two-agent two-strategy zero-sum games, such as Matching Pennies. Even for this simplest of benchmarks the best known bound for total regret, prior to our work, was the trivial one of $O(T)$, which is immediately applicable even to a non-learning agent. Based on a tight understanding of the geometry of the non-equilibrating trajectories in the dual space we prove a regret bound of $Θ(\sqrt{T})$ matching the well known optimal bound for adaptive step sizes in the online setting. This guarantee holds for all fixed step-sizes without having to know the time horizon in advance and adapt the fixed step-size accordingly. As a corollary, we establish that even with fixed learning rates the time-average of mixed strategies, utilities converge to their exact Nash equilibrium values.
Dynamic Regret Bounds for Online Omniprediction with Long Term Constraints
Department of Computer and Information Sciences, University of Pennsylvania(计算机与信息科学系,宾夕法尼亚大学);Department of Statistics and Data Science, University of Pennsylvania(统计与数据科学系,宾夕法尼亚大学)
Regret Minimization in Population Network Games: Vanishing Heterogeneity and Convergence to Equilibria
School of Mechanical Engineering, Northwestern Polytechnical University(西北工业大学机械工程学院);Department of Computing, Hong Kong Polytechnic University(香港理工大学计算机学院);Shanghai Artificial Intelligence Laboratory(上海人工智能实验室);School of Statistics and Mathematics, Yunnan University of Finance and Economics(云南财经大学统计与数学学院);School of Artificial Intelligence, Optics and Electronics (iOPEN), Northwestern Polytechnical University(西北工业大学人工智能、光学与电子学院(iOPEN));School of Cybersecurity, Northwestern Polytechnical University(西北工业大学网络安全学院)