数学物理学报(英文版) ›› 2020, Vol. 40 ›› Issue (5): 1429-1444.doi: 10.1007/s10473-020-0515-9

• 论文 • 上一篇    下一篇

PERIODIC POINTS AND NORMALITY CONCERNING MEROMORPHIC FUNCTIONS WITH MULTIPLICITY

邓炳茂1, 方明亮2, 王跃飞3,4   

  1. 1. School of Financial Mathematics and Statistics, Guangdong University of Finance, Guangzhou 510521, China;
    2. Department of Mathematics, Hangzhou Dianzi University, Hangzhou 310012, China;
    3. School of Mathematics and Statistics, Shenzhen University, Shenzhen 518060, China;
    4. Academy of Mathematics and Systems Science, Chinese Academy of Sciences, Beijing 100190, China
  • 收稿日期:2018-12-04 修回日期:2020-01-04 出版日期:2020-10-25 发布日期:2020-11-04
  • 通讯作者: Mingliang FANG E-mail:mlfang@hdu.edu.cn
  • 作者简介:Bingmao DENG,E-mail:dbmao2012@163.com;Yuefei WANG,E-mail:wangyf@math.ac.cn
  • 基金资助:
    The first author was supported by the NNSF of China (11901119, 11701188); The third author was supported by the NNSF of China (11688101).

PERIODIC POINTS AND NORMALITY CONCERNING MEROMORPHIC FUNCTIONS WITH MULTIPLICITY

Bingmao DENG1, Mingliang FANG2, Yuefei WANG3,4   

  1. 1. School of Financial Mathematics and Statistics, Guangdong University of Finance, Guangzhou 510521, China;
    2. Department of Mathematics, Hangzhou Dianzi University, Hangzhou 310012, China;
    3. School of Mathematics and Statistics, Shenzhen University, Shenzhen 518060, China;
    4. Academy of Mathematics and Systems Science, Chinese Academy of Sciences, Beijing 100190, China
  • Received:2018-12-04 Revised:2020-01-04 Online:2020-10-25 Published:2020-11-04
  • Contact: Mingliang FANG E-mail:mlfang@hdu.edu.cn
  • Supported by:
    The first author was supported by the NNSF of China (11901119, 11701188); The third author was supported by the NNSF of China (11688101).

摘要: In this article, two results concerning the periodic points and normality of meromorphic functions are obtained: (i) the exact lower bound for the numbers of periodic points of rational functions with multiple fixed points and zeros is proven by letting $R(z)$ be a non-polynomial rational function, and if all zeros and poles of $R(z)-z$ are multiple, then $R^k(z)$ has at least $k+1$ fixed points in the complex plane for each integer $k\ge 2$; (ii) a complete solution to the problem of normality of meromorphic functions with periodic points is given by letting $\mathcal{F}$ be a family of meromorphic functions in a domain $D$, and letting $k\ge 2$ be a positive integer. If, for each $f\in \mathcal{F}$, all zeros and poles of $f(z)-z$ are multiple, and its iteration $f^k$ has at most $k$ distinct fixed points in $D$, then $\mathcal{F}$ is normal in $D$. Examples show that all of the conditions are the best possible.

关键词: normality, iteration, periodic points

Abstract: In this article, two results concerning the periodic points and normality of meromorphic functions are obtained: (i) the exact lower bound for the numbers of periodic points of rational functions with multiple fixed points and zeros is proven by letting $R(z)$ be a non-polynomial rational function, and if all zeros and poles of $R(z)-z$ are multiple, then $R^k(z)$ has at least $k+1$ fixed points in the complex plane for each integer $k\ge 2$; (ii) a complete solution to the problem of normality of meromorphic functions with periodic points is given by letting $\mathcal{F}$ be a family of meromorphic functions in a domain $D$, and letting $k\ge 2$ be a positive integer. If, for each $f\in \mathcal{F}$, all zeros and poles of $f(z)-z$ are multiple, and its iteration $f^k$ has at most $k$ distinct fixed points in $D$, then $\mathcal{F}$ is normal in $D$. Examples show that all of the conditions are the best possible.

Key words: normality, iteration, periodic points

中图分类号: 

  • 30D45