Powered by OpenAIRE graph
Found an issue? Give us feedback
image/svg+xml art designer at PLoS, modified by Wikipedia users Nina, Beao, JakobVoss, and AnonMoos Open Access logo, converted into svg, designed by PLoS. This version with transparent background. http://commons.wikimedia.org/wiki/File:Open_Access_logo_PLoS_white.svg art designer at PLoS, modified by Wikipedia users Nina, Beao, JakobVoss, and AnonMoos http://www.plos.org/ Journal of Applied A...arrow_drop_down
image/svg+xml art designer at PLoS, modified by Wikipedia users Nina, Beao, JakobVoss, and AnonMoos Open Access logo, converted into svg, designed by PLoS. This version with transparent background. http://commons.wikimedia.org/wiki/File:Open_Access_logo_PLoS_white.svg art designer at PLoS, modified by Wikipedia users Nina, Beao, JakobVoss, and AnonMoos http://www.plos.org/
image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
zbMATH Open
Article . 2006
Data sources: zbMATH Open
Journal of Applied Analysis
Article . 2006 . Peer-reviewed
Data sources: Crossref
versions View all 2 versions
addClaim

Notes on Uniqueness of Meromorphic Functions

Notes on uniqueness of meromorphic functions
Authors: Lü, W.; Cao, J.;

Notes on Uniqueness of Meromorphic Functions

Abstract

In this paper, the authors prove (Theorem~1.1): Let \(f\), \(g\) be distinct nonconstant meromorphic functions and \(n\geq 10\) be an integer. Put \(h=f/g\). If \(E(\infty,f)=E(\infty,g)\) and \(E_{(3)}\bigl(1,f^n(f-1)f'\bigr)=E_{(3)}\bigl(1,g^n(g-1)g'\bigr)\), then \(f=R_n(1/h)\) and \(g=R_n(h)\) for the rational function \(R_n(w)=P_{n+1}(w)/P_{n+2}(w)\) with \(P_k(w)=(w^{k}-1)/k\). As its corollary, if one restricts both \(f\) and \(g\) to entire functions, the uniqueness \(f\equiv g\) is obtained from the \textit{set} equation \(E_{(3)}\bigl(1,f^n(f-1)f'\bigr)=E_{(3)}\bigl(1,g^n(g-1)g'\bigr)\) when \(n\geq 7\). Here \(E_{(k)}(a,\varphi)\) (\(k\in\mathbb{N}\cup\{\infty\}\), \(a\in\mathbb{C}\cup\{\infty\}\)) is the sequence of the \(a\)-points of a nonconstant meromorphic function~\(\varphi\) in~\(\mathbb{C}\) with multiplicity \(\leq k\), each points being repeated as many times as its multiplicity. Especially, \(E(a,\varphi)=E_{(\infty)}(a,\varphi)\). These results give extensions of some earlier results by \textit{M. L. Fang} and \textit{W. Hong} [Indian J. Pure Appl. Math. 32, No. 9, 1343--1348 (2001; Zbl 1005.30023)], \textit{H. L. Qiu} and \textit{Fang} [Bull. Korean Math. Soc. 41, No.1, 109-116 (2004; Zbl 1134.30325)], \textit{W. C. Lin} and \textit{H. X. Yi} in [Indian J. Pure Appl. Math. 35, No. 2, 121--132 (2004; Zbl 1056.30031)], and others. Related results are given by \textit{I. Lahiri} and \textit{N. Mandal} in [Int. J. Math. Math. Sci. 2005, No. 12, 1933--1942 (2005; Zbl 1084.30029)], too. The corollary itself seems to be proved also by \textit{I. Lahiri} and \textit{P. Sahoo} in [Georgian Math. J. 12, No. 1, 131--138 (2005; Zbl 1073.30022)]. One needs an additional assumption in order to exclude the case when \(f=R_n(1/h)\) and \(g=R_n(h)\) and then to conclude the uniqueness of transcendental meromorphic~\(f\) and~\(g\) under consideration. Some of the papers above limit the frequency of their poles with \(n\), such as \(\Theta(\infty,\varphi)>2/(n+1)\), since the \textit{deficiency} attains \(2/(n+1)\) for \(\varphi=R_n(h)\) with a suitable~\(h\). A proof of such results requires a \textit{variant} of the so-called Nevanlinna-Cartan Second Main Theorem for \textit{distinct} meromorphic functions~\(F\) and~\(G\) sharing \(1\)-points with \(FG\not\equiv 1\), as Lemma~2.2 in the paper under review. Then they apply their estimate to \(F=\Pi(f)\) and \(G=\Pi(g)\) with \(\Pi(\varphi):=\varphi^n(\varphi-1)\varphi'\). (For example, Lahiri and Mandal show that \(\Pi(f)\Pi(g)\not\equiv 1\) for any nonconstant meromorphic functions~\(f\) and~\(g\) when \(n\geq 5\).) This differential polynomial \(\Pi\bigl(\varphi(z)\bigr)\) is the derivative of \(P_{n+2}\bigl(\varphi(z)\bigr)-P_{n+1}\bigl(\varphi(z)\bigr)\) and the exceptional pair in Theorem~1.1, \(R_n(1/h)\) and \(R_n(h)\), is obtained when \(F\equiv G\) holds with \(h\not\equiv 1\). In fact, they prove that \(P_{n+2}(f)-P_{n+1}(f)\equiv P_{n+2}(g)-P_{n+1}(g)\) still holds, which implies directly the desired expression with \(h=f/g\). One could think it natural that the methods and discussions are overlapping those in many papers relating to the famous problems on \textit{uniqueness polynomials} posed by \textit{F. Gross} in [Complex Anal., Proc. Conf., Lexington 1976, Lect. Notes Math. 599, 51--67 (1977; Zbl 0357.30007)] and on differential polynomials by [\textit{W. K. Hayman}, Research problems in function theory. London: University of London. The Athlone Press (1967; Zbl 0158.06301)], respectively.

Country
United States
Related Organizations
Keywords

330, meromorphic function, uniqueness, sharing value, 510, Value distribution of meromorphic functions of one complex variable, Nevanlinna theory

  • BIP!
    Impact byBIP!
    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).
    0
    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.
    Average
    influence
    This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
    Average
    impulse
    This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
    Average
Powered by OpenAIRE graph
Found an issue? Give us feedback
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!
0
Average
Average
Average
bronze