Basic Relations Valid for the Bernstein Space $B^{p}_{\sigma}$ and Their Extensions to Functions from Larger Spaces with
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Basic Relations Valid for the Bernstein Space Bσ and Their Extensions to Functions from Larger Spaces with Error Estimates in Terms of Their Distances p from Bσ Paul L. Butzer · Gerhard Schmeisser · Rudolf L. Stens Received: 13 June 2012 / Revised: 16 January 2013 / Published online: 16 March 2013 © Springer Science+Business Media New York 2013
Abstract There are various basic relations (equations and inequalities) that hold in p Bernstein spaces Bσ but are no longer valid in larger spaces. However, when a function f is in some sense close to a Bernstein space, one may expect that the corresponding relation is not violated drastically. It should hold with a remainder that p involves the distance of f from Bσ . First we establish a hierarchy of spaces that generalize the Bernstein spaces and are suitable for our studies. It includes Hardy spaces, Sobolev spaces, Lipschitz classes and Fourier inversion classes. Next we introduce an appropriate metric for describing the distance of a function belonging to such a space from a Bernstein space. It will be used for estimating remainders and studying rates of convergence. In the main part, we present the desired extensions. Our considerations include the classical sampling formula by Whittaker-Kotel’nikov-Shannon, the sampling formula
Communicated by Hans G. Feichtinger. A preliminary version of this paper was presented by one of the authors (G. Schmeisser) as an invited one hour lecture at the First Bavaria-Québec Mathematical Meeting held at Montreal (November 30 to December 3, 2009) and conducted by R. Fournier and St. Ruscheweyh. The paper in its present form, but without the new results on derivative-free error estimates, was the basis of an invited lecture given jointly by two of the authors (P.L. Butzer and G. Schmeisser) at the workshop From Abstract to Computational Harmonic Analysis, held at Strobl (Austria, June 13–19, 2011) in honour of the 60th birthday of H.G. Feichtinger; this workshop was conducted by K. Gröchenig and T. Strohmer. P.L. Butzer · R.L. Stens Lehrstuhl A für Mathematik, RWTH Aachen University, 52056 Aachen, Germany P.L. Butzer e-mail: [email protected] R.L. Stens e-mail: [email protected] G. Schmeisser () Department of Mathematics, University of Erlangen-Nuremberg, 91058 Erlangen, Germany e-mail: [email protected]
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J Fourier Anal Appl (2013) 19:333–375
of Valiron-Tschakaloff, the differentiation formula of Boas, the reproducing kernel formula, the general Parseval formula, Bernstein’s inequality for the derivative and Nikol’ski˘ı’s inequality estimating the l p (Z) norm in terms of the Lp (R) norm. All the remainders are represented in terms of the Fourier transform of f and estimated from above by the new metric. Finally we show that the remainders can be continued to spaces where a Fourier transform need not exist and can be estimated in terms of the regularity of f . Keywords Non-bandlimited functions · Formulae with remainders · Derivative-free error estimates · Sampling formulae · Differentiation formula
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