Extremal problems on the class of convex functions of order −1/2

被引:0
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作者
Yusuf Abu Muhanna
Liulan Li
Saminathan Ponnusamy
机构
[1] American University of Sharjah,Department of Mathematics
[2] Hengyang Normal University,Department of Mathematics and Computational Science
[3] SETS (Society for Electronic Transactions and Security),Indian Statistical Institute (ISI), Chennai Centre
来源
Archiv der Mathematik | 2014年 / 103卷
关键词
Primary 30C65; 30C45; Secondary 30C20; 30C55; 31A05; 31B05; 31C05; Univalent; Convex; Starlike; Close-to-convex; Extreme points; Hayman index; Arclength; Zalcman functional; Harmonic function;
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摘要
Lawrence Zalcman’s conjecture states that if f(z)=z+∑n=2∞anzn\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${f(z)=z+\sum\nolimits_{n=2}^{\infty}a_{n}z^{n}}$$\end{document} is analytic and univalent in the unit disk |z|<1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${|z|<1}$$\end{document}, then |an2-a2n-1|≤(n-1)2,\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${|a_n^2-a_{2n-1}|\leq (n-1)^2,}$$\end{document} for each n≥2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${n\geq 2}$$\end{document}, with equality only for the Koebe function k(z)=z/(1-z)2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${k(z)=z/(1-z)^2}$$\end{document} and its rotations. This conjecture remains open although it has been verified for a few geometric subclasses of the class of univalent analytic functions. In this paper, we consider this problem for the family of normalized functions f analytic and univalent in the unit disk |z| < 1 satisfying the condition Re1+zf′′(z)f′(z)>-12for|z|<1.\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\rm Re }\left( 1+\frac{zf''(z)}{f'(z)}\right) > -\frac{1}{2}\,\,\,\,\,{\rm for}\,\,\,\,\,|z|<1.$$\end{document}Functions satisfying this condition are known to be convex in some direction (and hence close-to-convex and univalent) in |z| < 1. A few other related basic results and remarks about the Hayman index of functions in this family are also presented.
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页码:461 / 471
页数:10
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