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The statistical complexity of early-stopped mirror descent

Abstract:
Recently there has been a surge of interest in understanding implicit regularization properties of iterative gradient-based optimization algorithms. In this paper, we study the statistical guarantees on the excess risk achieved by early-stopped unconstrained mirror descent algorithms applied to the unregularized empirical risk. We consider the set-up of learning linear models and kernel methods for strongly convex and Lipschitz loss functions while imposing only boundedness conditions on the unknown data-generating mechanism. By completing an inequality that characterizes convexity for the squared loss, we identify an intrinsic link between offset Rademacher complexities and potential-based convergence analysis of mirror descent methods. Our observation immediately yields excess risk guarantees for the path traced by the iterates of mirror descent in terms of offset complexities of certain function classes depending only on the choice of the mirror map, initialization point, step size and the number of iterations. We apply our theory to recover, in a clean and elegant manner via rather short proofs, some of the recent results in the implicit regularization literature while also showing how to improve upon them in some settings.
Publication status:
Published
Peer review status:
Peer reviewed

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Publisher copy:
10.1093/imaiai/iaad047

Authors

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Institution:
University of Oxford
Division:
MPLS
Department:
Computer Science
Role:
Author
ORCID:
0000-0002-2300-4819
More by this author
Institution:
University of Oxford
Division:
MPLS
Department:
Statistics
Oxford college:
University College
Role:
Author
ORCID:
0000-0001-7772-4160


Publisher:
Oxford University Press
Journal:
Information and Inference: A Journal of the IMA More from this journal
Volume:
12
Issue:
4
Pages:
3010-3041
Publication date:
2023-11-23
Acceptance date:
2023-10-22
DOI:
EISSN:
2049-8772
ISSN:
2049-8764


Language:
English
Keywords:
Pubs id:
1588677
Local pid:
pubs:1588677
Deposit date:
2024-01-03
ARK identifier:

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