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Beyond Worst-Case Analysis in Stochastic Approximation: Moment Estimation Improves Instance Complexity
Jingzhao Zhang · Hongzhou Lin · Subhro Das · Suvrit Sra · Ali Jadbabaie

Wed Jul 20 07:55 AM -- 08:00 AM (PDT) @ Room 327 - 329

We study oracle complexity of gradient based methods for stochastic approximation problems. Though in many settings optimal algorithms and tight lower bounds are known for such problems, these optimal algorithms do not achieve the best performance when used in practice. We address this theory-practice gap by focusing on \emph{instance-dependent complexity} instead of worst case complexity. In particular, we first summarize known instance-dependent complexity results and categorize them into three levels. We identify the domination relation between different levels and propose a fourth instance-dependent bound that dominates existing ones. We then provide a sufficient condition according to which an adaptive algorithm with moment estimation can achieve the proposed bound without knowledge of noise levels. Our proposed algorithm and its analysis provide a theoretical justification for the success of moment estimation as it achieves improved instance complexity.

Author Information

Jingzhao Zhang (Tsinghua University)
Hongzhou Lin (Amazon)
Subhro Das (MIT-IBM Watson AI Lab, IBM Research)

Subhro Das is a Research Staff Member and Manager at the MIT-IBM AI Lab, IBM Research, Cambridge MA. As a Principal Investigator (PI), he works on developing novel AI algorithms in collaboration with MIT. He is a Research Affiliate at MIT, co-leading IBM's engagement in the MIT Quest for Intelligence. He serves as the Chair of the AI Learning Professional Interest Community (PIC) at IBM Research. His research interests are broadly in the areas of Trustworthy ML, Reinforcement Learning and ML Optimization. At the MIT-IBM AI Lab, he works on developing novel AI algorithms for uncertainty quantification and human-centric AI systems; robust, accelerated, online & distributed optimization; and, safe, unstable & multi-agent reinforcement learning. He led the Future of Work initiative within IBM Research, studying the impact of AI on the labor market and developing AI-driven recommendation frameworks for skills and talent management. Previously, at the IBM T.J. Watson Research Center in New York, he worked on developing signal processing and machine learning based predictive algorithms for a broad variety of biomedical and healthcare applications. He received MS and PhD degrees in Electrical and Computer Engineering from Carnegie Mellon University in 2014 and 2016, respectively, and Bachelors (B.Tech.) degree in Electronics & Electrical Communication Engineering from Indian Institute of Technology Kharagpur in 2011.

Suvrit Sra (MIT & Macro-Eyes)
Ali Jadbabaie (Massachusetts Institute of Technology)

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