Acta mathematica scientia,Series B ›› 2020, Vol. 40 ›› Issue (5): 1429-1444.doi: 10.1007/s10473-020-0515-9

• Articles • Previous Articles     Next Articles

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).

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

CLC Number: 

  • 30D45
Trendmd