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Approximation of functions: Optimal sampling and complexity

Published online by Cambridge University Press:  19 June 2026

David Krieg
Affiliation:
Faculty of Computer Science and Mathematics, University of Passau, 94032 Passau, Germany E-mail: david.krieg@uni-passau.de
Mario Ullrich
Affiliation:
Department of Quantum Computing & Institute of Analysis, Johannes Kepler University, 4040 Linz, Austria E-mail: mario.ullrich@jku.at
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Abstract

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We consider the approximation or recovery of functions based on a finite number of function evaluations. This is a well-studied problem in optimal recovery, machine learning and numerical analysis in general, but many fundamental insights were obtained only recently. We discuss different aspects of the information-theoretic limit that appears because of the limited data available, as well as algorithms and sampling strategies that come as close to it as possible.

We also discuss (optimal) sampling in a broader sense, allowing other types of measurements that may be nonlinear, adaptive and random, and present several relations between the different settings in the spirit of information-based complexity. We hope that this article will provide both a basic introduction to the subject and a contemporary summary of the current state of research.

Information

Type
Research Article
Creative Commons
Creative Common License - CCCreative Common License - BY
This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0), which permits unrestricted re-use, distribution and reproduction, provided the original article is properly cited.
Copyright
© The Author(s), 2026. Published by Cambridge University Press