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Mathematische Zeitschrift
Article . 1980 . Peer-reviewed
License: Springer TDM
Data sources: Crossref
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zbMATH Open
Article . 1980
Data sources: zbMATH Open
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Nonvanishing univalent functions

Authors: Duren, Peter L.; Schober, Glenn;

Nonvanishing univalent functions

Abstract

The class S of functions g(z) = z + c 2 z 2 + c 3 z 3 + ... analytic and univalent in the unit disk Izr < 1 has been thoroughly studied, and its properties are well known. Our purpose is to investigate another class of functions which, by contrast, seems to have been rather neglected. This is the class S o of functions f ( z ) = 1 + a 1 z + a 2 z Z + . . , analytic, univalent, and nonvanishing in the unit disk, normalized by the condition f(0) = 1. It will become apparent that S O is closely related to the more familiar class S and is in some ways easier to handle. After making a few preliminary observations, we adapt the elementary method of Brickman [23 to obtain information about the extreme points and support points of S o. We then use Schiffer's method of boundary variation to consider a wide class of extremal problems and to study the support points of S o in greater depth. Whereas the geometry of the arcs omitted by extreme points and support points of S is related to the families of linear rays and circles centered at the origin, it turns out that the corresponding geometry for S o is related to the families of ellipses and hyperbolas with loci at 0 and 1. The paper concludes with a detailed study of the specific linear extremal problem rain Re{f(~)}, which provides an interesting family of support points in S 0.

Countries
United States, Germany
Keywords

Science, Extremal problems for conformal and quasiconformal mappings, variational methods, General theory of univalent and multivalent functions of one complex variable, Article, 510.mathematics, univalent functions, support points, extremal problems for conformal and quasiconformal mappings, variational methods, extreme points, General, Mathematics

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selected citations
These citations are derived from selected sources.
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
9
Average
Top 10%
Average
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