Analytic function: Difference between revisions

Revision as of 21:07, 22 August 2020

Revision as of 12:35, 30 August 2020

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Complex analytic functions are exactly equivalent to [[Holomorphic function|holomorphic functions]], and are thus much more easily characterized.

For the case of an analytic function with several variables (see below), the real analyticity can be characterized using the [[Fourier–Bros–Iagolnitzer transform]]. The

In thirdthe characterizationmultivariable hascase, alsoreal analytic functions satisfy a direct generalization forof the multivariatethird casecharacterization. Let <math>U \subset \R^n</math> be an open set, and let <math>f: U \to \R</math>.<ref>{{Cite journal|last=Komatsu|first=Hikosaburo|date=1960|title=A characterization of real analytic functions|url=https://projecteuclid.org/euclid.pja/1195524081|journal=Proceedings of the Japan Academy|language=EN|volume=36|issue=3|pages=90–93|doi=10.3792/pja/1195524081|issn=0021-4280|doi-access=free}}</ref>

Then <math>f</math> is real analytic on <math>U</math> if and only if <math>f \in C^\infty(U)</math> and for every compact <math>K \subseteq U</math> there exists a constant <math>C</math> such that for every multi-index <math>\alpha \in \Z_{\geq 0}^n</math> the following bound holds<ref>{{Cite web|title=Gevrey class - Encyclopedia of Mathematics|url=https://encyclopediaofmath.org/wiki/Gevrey_class#References|access-date=2020-08-30|website=encyclopediaofmath.org}}</ref><blockquote><math> \sup_{x \in K} \left | \frac{\partial^\alpha f}{\partial x^\alpha}(x) \right | \leq C^{|\alpha|+1} |\alpha!|</math></blockquote>

==Properties of analytic functions==