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We study the recovery of functions in various norms, including $L_p$ with $1\le p\le\infty$, based on function evaluations. We obtain worst case error bounds for general classes of functions in terms of the best $L_2$-approximation from a…

Numerical Analysis · Mathematics 2025-12-23 David Krieg , Kateryna Pozharska , Mario Ullrich , Tino Ullrich

Function values are, in some sense, "almost as good" as general linear information for $L_2$-approximation (optimal recovery, data assimilation) of functions from a reproducing kernel Hilbert space. This was recently proved by new upper…

Numerical Analysis · Mathematics 2022-03-23 Aicke Hinrichs , David Krieg , Erich Novak , Jan Vybiral

In this paper we study the sampling recovery problem for certain relevant multivariate function classes which are not compactly embedded into $L_\infty$. Recent tools relating the sampling numbers to the Kolmogorov widths in the uniform…

Numerical Analysis · Mathematics 2022-10-05 Glenn Byrenheid , Serhii A. Stasyuk , Tino Ullrich

In this paper we present results on asymptotic characteristics of multivariate function classes in the uniform norm. Our main interest is the approximation of functions with mixed smoothness parameter not larger than $1/2$. Our focus will…

Functional Analysis · Mathematics 2021-11-01 Vladimir Temlyakov , Tino Ullrich

We studied linear weighted sampling algorithms and their optimality for approximate recovery of functions with mixed smoothness on $\mathbb{R}^d$ from a set of $n$ their sampled values. Functions to be recovered are in weighted Sobolev…

Numerical Analysis · Mathematics 2025-11-11 Dinh Dũng

It is known that results on universal sampling discretization of the square norm are useful in sparse sampling recovery with error measured in the square norm. In this paper we demonstrate how known results on universal sampling…

Numerical Analysis · Mathematics 2023-07-11 V. N. Temlyakov

In this paper we consider the $L_q$-approximation of multivariate periodic functions $f$ with $L_p$-bounded mixed derivative (difference). The (possibly non-linear) reconstruction algorithm is supposed to recover the function from function…

Numerical Analysis · Mathematics 2017-03-02 Glenn Byrenheid , Tino Ullrich

Recently, it was discovered that for a given function class $\mathbf{F}$ the error of best linear recovery in the square norm can be bounded above by the Kolmogorov width of $\mathbf{F}$ in the uniform norm. That analysis is based on deep…

Numerical Analysis · Mathematics 2023-05-17 F. Dai , V. Temlyakov

We consider the task of recovering a Sobolev function on a connected compact Riemannian manifold $M$ when given a sample on a finite point set. We prove that the quality of the sample is given by the $L_\gamma(M)$-average of the geodesic…

Numerical Analysis · Mathematics 2024-09-23 David Krieg , Mathias Sonnleitner

We show that there are sampling projections on arbitrary $n$-dimensional subspaces of $B(D)$ with at most $2n$ samples and norm of order $\sqrt{n}$, where $B(D)$ is the space of complex-valued bounded functions on a set $D$. This gives a…

Functional Analysis · Mathematics 2025-10-02 David Krieg , Kateryna Pozharska , Mario Ullrich , Tino Ullrich

In this work, we consider the approximate reconstruction of high-dimensional periodic functions based on sampling values. As sampling schemes, we utilize so-called reconstructing multiple rank-1 lattices, which combine several preferable…

Numerical Analysis · Mathematics 2019-05-14 Lutz Kämmerer , Toni Volkmer

Results on asymptotic characteristics of classes of functions with mixed smoothness are obtained in the paper. Our main interest is in estimating the Kolmogorov widths of classes with small mixed smoothness. We prove the corresponding…

Numerical Analysis · Mathematics 2020-12-21 V. Temlyakov , T. Ullrich

We provide a new upper bound for sampling numbers $(g_n)_{n\in \mathbb{N}}$ associated to the compact embedding of a separable reproducing kernel Hilbert space into the space of square integrable functions. There are universal constants…

Numerical Analysis · Mathematics 2021-02-11 Nicolas Nagel , Martin Schäfer , Tino Ullrich

We consider recovering a function $f : D \rightarrow \mathbb{C}$ in an $n$-dimensional linear subspace $\mathcal{P}$ from i.i.d. pointwise samples via (weighted) least-squares estimators. Different from most works, we assume the cost of…

Numerical Analysis · Mathematics 2025-06-06 Ben Adcock

In this paper we study $L_2$-norm sampling discretization and sampling recovery of complex-valued functions in RKHS on $D \subset \R^d$ based on random function samples. We only assume the finite trace of the kernel (Hilbert-Schmidt…

Numerical Analysis · Mathematics 2021-05-03 Moritz Moeller , Tino Ullrich

Using techniques developed recently in the field of compressed sensing we prove new upper bounds for general (nonlinear) sampling numbers of (quasi-)Banach smoothness spaces in $L^2$. In particular, we show that in relevant cases such as…

Numerical Analysis · Mathematics 2023-08-02 Thomas Jahn , Tino Ullrich , Felix Voigtlaender

We tensorize the Faber spline system from [14] to prove sequence space isomorphisms for multivariate function spaces with higher mixed regularity. The respective basis coefficients are local linear combinations of discrete function values…

Functional Analysis · Mathematics 2020-04-08 Nadiia Derevianko , Tino Ullrich

Recently, there was a substantial progress in the problem of sampling recovery on function classes with mixed smoothness. Mostly, it has been done by proving new and sometimes optimal upper bounds for both linear sampling recovery and for…

Numerical Analysis · Mathematics 2025-05-29 A. Gasnikov , V. Temlyakov

This paper constructs unique compactly supported functions in Sobolev spaces that have minimal norm, maximal support, and maximal central value, under certain renormalizations. They may serve as optimized basis functions in interpolation or…

Numerical Analysis · Mathematics 2024-09-04 Robert Schaback

This paper addresses the problem of regression to reconstruct functions, which are observed with superimposed errors at random locations. We address the problem in reproducing kernel Hilbert spaces. It is demonstrated that the estimator,…

Statistics Theory · Mathematics 2021-08-17 Paul Dommel , Alois Pichler
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