提出通用收敛定理,统一多类随机逼近方法。
An abstract effective convergence theorem for stochastic processes, with applications to stochastic approximation
- 基于松弛超鞅条件,用通用模量τ刻画解的期望唯一性。
- 给出高一致性的收敛速率,仅依赖τ和少量数据。
- 适用于随机逼近中的经典定理,可导出线性收敛率。
我们给出了一个关于满足松弛超鞅条件的随机过程渐近行为的通用定理。其突出特点是,在比传统随机逼近文献更高的抽象层次与更广的适用范围内,提供了定量收敛保证,特别以一般模量τ来形式化表达相关解期望唯一性的有效版本。收敛速率高度一致,除τ外仅依赖极少数数据。随后,我们通过该结果作为统一框架,推导出随机逼近中多个关键概念与定理的新量化版本,包括Robbins-Siegmund定理、Dvoretzky收敛定理以及随机拟Fejér单调序列的收敛性,后者在新颖且高度一般的度量背景下表述。文中还分析了若干特例,可构造快速甚至线性收敛速率。本文讨论了结果及相关方法在随机逼近中的多种应用,并在作者相关工作中明确推导。
原文摘要 · Abstract (English)
We provide a general theorem on the asymptotic behavior of stochastic processes that conform to a relaxed supermartingale condition. The distinguishing feature of our result is that it provides quantitative convergence guarantees at a much higher level of abstraction and generality than is typically seen in the stochastic approximation literature, formulated in particular in terms of a general modulus $τ$ that, on an intuitive level, captures an effective variant of the uniqueness in expectation of associated solutions. Our convergence rate is highly uniform, depending on very few data beyond $τ$. We then demonstrate the utility of our result as a unifying framework by deriving new quantitative versions of several key concepts and theorems from stochastic approximation, including the Robbins-Siegmund theorem, Dvoretzky's convergence theorem, and the convergence of stochastic quasi-Fejér monotone sequences, the latter formulated in a novel and highly general metric context. Throughout, we isolate and discuss special cases of our results which allow for the construction of fast, and in particular linear, rates. Various applications of our results and our general methodology to stochastic approximation are discussed, and in particular explicitly derived in related work of the authors.
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