Abstract
The aim of this paper is to investigate the cone of non-negative, radial, positive-definite functions in the set of continuous functions on ℝd. Elements of this cone admit a Choquet integral representation in terms of the extremals. The main feature of this article is to characterize some large classes of such extremals. In particular, we show that there are many other extremals than the Gaussians, thus disproving a conjecture of G. Choquet, and that no reasonable conjecture can be made on the full set of extremals.
The last feature of this article is to show that many characterizations of positive definite functions available in the literature are actually particular cases of the Choquet integral representations we obtain.
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Communicated by Gerald B. Folland.
The authors wish to thank E.G.F. Thomas for valuable conversations and G. Godefroy for mentioning the problem to them.
M. Matolcsi was supported by Hungarian National Foundation for Scientific Research (OTKA), Grants No. PF-64061, T-04930, and by a Visiting Professorship of the University of Orleans, October 2007.
The third author was supported by Hungarian National Science Foundation, grant no.’s OTKA # T 049301, K 061908 and K 072731.
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Jaming, P., Matolcsi, M. & Révész, S.G. On the Extremal Rays of the Cone of Positive, Positive Definite Functions. J Fourier Anal Appl 15, 561–582 (2009). https://doi.org/10.1007/s00041-008-9057-6
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DOI: https://doi.org/10.1007/s00041-008-9057-6