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On best localized bandlimited functions
Authors:S Norvidas
Institution:(1) Institute of Mathematics and Informatics, Akademijos 4, 08663 Vilnius, Lithuania
Abstract:Let, for σ > 0, 
$$\mathcal{B}_\sigma  $$
be the set of complex functions fL 1 (ℝ) with the Fourier transforms 
$$\hat f(x)\smallint _\mathbb{R} e^{ - 2\pi ixt} f(t)dt$$
vanishing outside the interval −σ; σ]. In this paper, we study the problem of the best approximation of the Dirac function δ (which has the Fourier transform with widest support supp 
$$(\hat \delta ) = \mathbb{R}$$
) by functions 
$$f \in \mathcal{B}_\sigma  $$
. More precisely, we consider the quantity inf 
$$\{ \sum _{n \in \mathbb{Z}} |f(n)|:f \in \mathcal{B}_\sigma  ,f(0) = 1\} $$
and its extremal functions 
$$f \in \mathcal{B}_\sigma  $$
. __________ Translated from Lietuvos Matematikos Rinkinys, Vol. 46, No. 4, pp. 548–564, October–December, 2006.
Keywords:Fourier transform  bandlimited functions  best localization  spectral synthesis sets  Bohr inequality  Poisson summation formula  sine-type entire functions
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