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Understanding Riemannian Acceleration via a Proximal Extragradient Framework
Proceedings of Thirty Fifth Conference on Learning Theory, PMLR 178:2924-2962, 2022.
Abstract
We contribute to advancing the understanding of Riemannian accelerated gradient methods. In particular, we revisit “\emph{Accelerated Hybrid Proximal Extragradient}” (A-HPE), a powerful framework for obtaining Euclidean accelerated methods \citep{monteiro2013accelerated}. Building on A-HPE, we then propose and analyze Riemannian A-HPE. The core of our analysis consists of two key components: (i) a set of new insights into Euclidean A-HPE itself; and (ii) a careful control of metric distortion caused by Riemannian geometry. We illustrate our framework by obtaining a few existing and new Riemannian accelerated gradient methods as special cases, while characterizing their acceleration as corollaries of our main results.