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Extension of positive definite functions
Journal article   Open access   Peer reviewed

Extension of positive definite functions

Palle E.T Jorgensen and Robert Niedzialomski
Journal of mathematical analysis and applications, Vol.422(1), pp.712-740
02/01/2015
DOI: 10.1016/j.jmaa.2014.09.002
url
https://doi.org/10.1016/j.jmaa.2014.09.002View
Published (Version of record) Open Access

Abstract

Let Ω⊂Rn be an open, connected subset of Rn, and let F:Ω−Ω→C, where Ω−Ω={x−y:x,y∈Ω}, be a continuous positive definite function. We give necessary and sufficient conditions for F to have an extension to a continuous positive definite function defined on the entire Euclidean space Rn. The conditions are formulated in terms of existence of a unitary representations of Rn whose generators extend a certain system of unbounded Hermitian operators defined on a Hilbert space associated to F. Different positive definite extensions correspond to different unitary representations.
Commuting selfadjoint extension Unitary representation Reproducing kernel Hilbert space Symmetric (Hermitian) unbounded operator Spectral resolution Positive definite function

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