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arXiv 1908.00261cs.LGstat.ML
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策略梯度方法理论:最优性、近似性与分布偏移

On the Theory of Policy Gradient Methods: Optimality, Approximation, and Distribution Shift

Microsoft Research(微软研究院);University of Washington(华盛顿大学);Princeton University(普林斯顿大学);University of California San Diego(加州大学圣地亚哥分校)

Alekh Agarwal, Sham M. Kakade, Jason D. Lee, Gaurav Mahajan

摘要:

策略梯度方法是解决具有大状态和/或动作空间的强化学习问题的最有效方法之一。然而,人们对它们最基本的理论收敛性质知之甚少,包括:它们是否收敛到全局最优解以及收敛速度有多快,或者它们如何处理由于使用一类受限的参数策略而导致的近似误差。这项工作提供了可证明的表征的计算,近似,和样本大小属性的策略梯度方法的背景下,折扣马尔可夫决策过程(MDP)。我们专注于两者:“表格”策略参数化,其中最优策略包含在类中,并且我们显示全局收敛到最优策略;和参数策略类(考虑对数线性和神经策略类),其可能不包含最优策略,并且我们提供不可知的学习结果。这项工作的一个核心贡献是在提供近似保证,是平均情况下-避免明确的最坏情况下的依赖关系的状态空间的大小-通过正式连接到监督学习下分布偏移。这种表征显示了估计误差、近似误差和探索(通过精确定义的条件数表征)之间的重要相互作用。

英文摘要:

Policy gradient methods are among the most effective methods in challenging reinforcement learning problems with large state and/or action spaces. However, little is known about even their most basic theoretical convergence properties, including: if and how fast they converge to a globally optimal solution or how they cope with approximation error due to using a restricted class of parametric policies. This work provides provable characterizations of the computational, approximation, and sample size properties of policy gradient methods in the context of discounted Markov Decision Processes (MDPs). We focus on both: "tabular" policy parameterizations, where the optimal policy is contained in the class and where we show global convergence to the optimal policy; and parametric policy classes (considering both log-linear and neural policy classes), which may not contain the optimal policy and where we provide agnostic learning results. One central contribution of this work is in providing approximation guarantees that are average case -- which avoid explicit worst-case dependencies on the size of state space -- by making a formal connection to supervised learning under distribution shift. This characterization shows an important interplay between estimation error, approximation error, and exploration (as characterized through a precisely defined condition number).

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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