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Journal of Mathematical Analysis and Applications
Article
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Journal of Mathematical Analysis and Applications
Article . 1997
License: Elsevier Non-Commercial
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Journal of Mathematical Analysis and Applications
Article . 1997 . Peer-reviewed
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zbMATH Open
Article . 1997
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Partial Sums of Starlike and Convex Functions

Partial sums of starlike and convex functions
Authors: Silverman, H;

Partial Sums of Starlike and Convex Functions

Abstract

Let \(S\) be the class of functions \(f:f(z)= z+\sum^\infty_{k=2} a_kz^k\) that are analytic in the unit disc \(E\). Let \(S^*(\alpha)\) and \(K(\alpha)\), respectively, be the subclasses of \(S\) which consist of starlike and convex functions of order \(\alpha, 0\leq\alpha <1\). A sufficient condition for \(f\) to be in \(S^*(\alpha)\) is that \(\sum^\infty_{k=2} (k-\alpha) | a_k |\leq 1-\alpha\) and to be in \(K(\alpha)\) is that \(\sum^\infty_{k=2} K(k-\alpha) | a_k|\leq 1- \alpha.\) In this paper, the ratio of a function \(f\) to its sequence of partial sums \(f_n(z)= z+ \sum^n_{k=2} a_kz^k\) is studied when the coefficients of \(f\) are sufficiently small to satisfy one of these conditions. Sharp lower bounds for \(\text{Re} \left\{{f(z) \over f_n(z)}\right\}\), \(\text{Re} \left\{{f_n(z) \over f(z)}\right\}\), \(\text{Re} \left\{{f'(z) \over f_n'(z)}\right\}\) and \(\text{Re} \left\{ {f_n'(z) \over f'(z)}\right\}\) are determined when the coefficients \(\{a_k\}\) are small.

Related Organizations
Keywords

Special classes of univalent and multivalent functions of one complex variable (starlike, convex, bounded rotation, etc.), convex functions, partial sums, Applied Mathematics, starlike, Analysis

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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!
90
Top 1%
Top 1%
Average
hybrid