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In [[mathematics]], the '''Nevanlinna class''' is a class of [[Function (mathematics)|functions]] defined on a [[Region (analysis)|region]] of the [[complex plane]]. Functions in the class have positive [[Subharmonic function#Harmonic majorants of subharmonic functions|harmonic majorants]] and hence are also said to be of '''bounded type'''. | |||
More formally, let <math>\Omega</math> be a region. A function <math>f</math> is said to be of ''bounded type'' on <math>\Omega</math> if <math>f</math> is [[Analytic function|analytic]] on <math>\Omega</math> and <math>\log^+|f(z)|</math> has a harmonic majorant on <math>\Omega</math> (where <math>\log^+(x)=\max\{0,\log(x)\}</math>). | |||
The class of all such <math>f</math> on <math>\Omega</math> is commonly denoted <math>N(\Omega)</math> and is sometimes called the ''[[Rolf Nevanlinna|Nevanlinna]] class'' for <math>\Omega</math>. The Nevanlinna class includes all the [[Hardy class]]es. | |||
'''Theorem''' ''A sufficient condition for <math>f</math> to be of bounded type on <math>\Omega</math> is that <math>f=g/u</math> where <math>u</math> and <math>g</math> are bounded and analytic on <math>\Omega</math> with <math>0<|u|</math>. If <math>\Omega</math> is [[simply connected]] the condition is also necessary.'' | |||
==See also== | |||
*[[De Branges space]] | |||
*[[Rolf Nevanlinna]] | |||
== References == | |||
<!--- See http://en.wikipedia.org/wiki/Wikipedia:Footnotes on how to create references using <ref></ref> tags which will then appear here automatically --> | |||
{{Reflist}} | |||
* {{cite book | title=Functions of a Complex Variable II | volume=159 | series=[[Graduate Texts in Mathematics]] | publisher=[[Springer-Verlag]] | isbn=0-387-94460-5 | first=John B. | last=Conway | authorlink=John B. Conway | page=273 }} | |||
* {{cite book | |||
|last1 = Rosenblum | |||
|first1 = Marvin | |||
|last2 = Rovnyak | |||
|first2 = James | |||
|title = Topics in Hardy classes and univalent functions | |||
|series = Birkhauser Advanced Texts: Basel Textbooks | |||
|publisher = Birkhauser Verlag | |||
|address = Basel | |||
|year = 1994 | |||
}} | |||
{{DEFAULTSORT:Bounded Type (Mathematics)}} | |||
[[Category:Complex analysis]] | |||
[[Category:Special functions]] | |||
[[Category:Types of functions]] | |||
[[Category:Articles created via the Article Wizard]] | |||
Revision as of 09:13, 3 September 2012
Template:Cleanup In mathematics, the Nevanlinna class is a class of functions defined on a region of the complex plane. Functions in the class have positive harmonic majorants and hence are also said to be of bounded type.
More formally, let be a region. A function is said to be of bounded type on if is analytic on and has a harmonic majorant on (where ).
The class of all such on is commonly denoted and is sometimes called the Nevanlinna class for . The Nevanlinna class includes all the Hardy classes.
Theorem A sufficient condition for to be of bounded type on is that where and are bounded and analytic on with . If is simply connected the condition is also necessary.
See also
References
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