arXiv Machine Learning By Siddharth Chandak

Concentration and Mean-Square Bounds for Contractive Stochastic Approximation: A Unified Elementary Approach

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arXiv:2607. 17595v1 Announce Type: new Abstract: We establish mean-square and concentration bounds for stochastic approximation (SA) with arbitrary norm contractive mappings, under a multiplicative noise model where the noise may scale affinely with the norm of the iterates, and the iterates are potentially unbounded.

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arXiv Statistics ML
Sep 25

Shrinking-Tube Concentration for Adaptive Markovian Stochastic Approximation

The paper establishes a shrinking‑tube concentration bound for projected stochastic approximation driven by an adaptive Markov chain, guaranteeing that after a chosen time every iterate stays within a tolerance that tightens over time. The bound’s probability of any exit after that time decays polynomially, and a matching lower bound shows this exponent is optimal under finite second moments. Extensions to recursions with martingale‑difference noise and predictable bias reveal how noise scale and bias affect exit‑probability decay and tube shrinkage, with applications to inventory learning and numerical gradient accuracy.

By Jin Li, Ye Luo, Xiaowei Zhang