Normal families and shared values of meromorphic functions

Mingliang Fang; Lawrence Zalcman

Displaying similar documents to “Normal families and shared values of meromorphic functions”

Normality criteria and multiple values II

Yan Xu, Jianming Chang (2011)

Annales Polonici Mathematici

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Let ℱ be a family of meromorphic functions defined in a domain D, let ψ (≢ 0, ∞) be a meromorphic function in D, and k be a positive integer. If, for every f ∈ ℱ and z ∈ D, (1) f≠ 0, $f^{(k)} \neq 0$ ; (2) all zeros of $f^{(k)} - ψ$ have multiplicities at least (k+2)/k; (3) all poles of ψ have multiplicities at most k, then ℱ is normal in D.

Finiteness of meromorphic functions on an annulus sharing four values regardless of multiplicity

Duc Quang Si, An Hai Tran (2020)

Mathematica Bohemica

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This paper deals with the finiteness problem of meromorphic funtions on an annulus sharing four values regardless of multiplicity. We prove that if three admissible meromorphic functions $f_{1}$ , $f_{2}$ , $f_{3}$ on an annulus $𝔸 (R_{0})$ share four distinct values regardless of multiplicity and have the of positive counting function, then $f_{1} = f_{2}$ or $f_{2} = f_{3}$ or $f_{3} = f_{1}$ . This result deduces that there are at most two admissible meromorphic functions on an annulus sharing a value with multiplicity truncated to level $2$ and sharing...

On the value distribution of differential polynomials of meromorphic functions

Yan Xu, Huiling Qiu (2010)

Annales Polonici Mathematici

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Let f be a transcendental meromorphic function of infinite order on ℂ, let k ∈ ℕ and $φ = R e^{P}$ , where R ≢ 0 is a rational function and P is a polynomial, and let $a ₀, a ₁, . . ., a_{k - 1}$ be holomorphic functions on ℂ. If all zeros of f have multiplicity at least k except possibly finitely many, and $f = 0 \Leftrightarrow f^{(k)} + a_{k - 1} f^{(k - 1)} + \dots + a ₀ f = 0$ , then $f^{(k)} + a_{k - 1} f^{(k - 1)} + \dots + a ₀ f - φ$ has infinitely many zeros.

Bounds for the derivative of certain meromorphic functions and on meromorphic Bloch-type functions

Bappaditya Bhowmik, Sambhunath Sen (2024)

Czechoslovak Mathematical Journal

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It is known that if $f$ is holomorphic in the open unit disc $𝔻$ of the complex plane and if, for some $c > 0$ , $| f (z) | \leq {1 / (1 - | z |}^{2})^{c}$ , $z \in 𝔻$ , then $| f^{'} {(z) | \leq 2 (c + 1) / (1 - | z |}^{2})^{c + 1}$ . We consider a meromorphic analogue of this result. Furthermore, we introduce and study the class of meromorphic Bloch-type functions that possess a nonzero simple pole in $𝔻$ . In particular, we obtain bounds for the modulus of the Taylor coefficients of functions in this class.

Uniqueness of meromorphic functions concerning value sharing of nonlinear differential monomials

Sujoy Majumder, Rajib Mandal (2020)

Mathematica Bohemica

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With the idea of normal family we study the uniqueness of meromorphic functions $f$ and $g$ when $f^{n} {(f^{(k)})}^{m} - p$ and $g^{n} {(g^{(k)})}^{m} - p$ share two values, where $p$ is any nonzero polynomial. The result of this paper significantly improves and generalizes the result due to A. Banerjee and S. Majumder (2018).

On zeros of differences of meromorphic functions

Yong Liu, HongXun Yi (2011)

Annales Polonici Mathematici

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Let f be a transcendental meromorphic function and $g (z) = f (z + c ₁) + \dots + f (z + c_{k}) - k f (z)$ and $g_{k} (z) = f (z + c ₁) \dots f (z + c_{k}) - f^{k} (z)$ . A number of results are obtained concerning the exponents of convergence of the zeros of g(z), $g_{k} (z)$ , g(z)/f(z), and $g_{k} (z) / f^{k} (z)$ .

Universal sequences for Zalcman’s Lemma and $Q_{m}$ -normality

Shahar Nevo (2005)

Annales Polonici Mathematici

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We prove the existence of sequences ${ϱ ₙ}_{n = 1}^{\infty}$ , ϱₙ → 0⁺, and ${z ₙ}_{n = 1}^{\infty}$ , |zₙ| = 1/2, such that for every α ∈ ℝ and for every meromorphic function G(z) on ℂ, there exists a meromorphic function $F (z) = F_{G, α} (z)$ on ℂ such that $ϱ ₙ^{α} F (n z ₙ + n ϱ ₙ ζ)$ converges to G(ζ) uniformly on compact subsets of ℂ in the spherical metric. As a result, we construct a family of functions meromorphic on the unit disk that is $Q_{m}$ -normal for no m ≥ 1 and on which an extension of Zalcman’s Lemma holds.

On certain subclasses of multivalently meromorphic close-to-convex maps

K. S. Padmanabhan (1998)

Annales Polonici Mathematici

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Let Mₚ denote the class of functions f of the form $f (z) = 1 / z^{p} + \sum_{k = 0}^{\infty} a ₖ z^{k}$ , p a positive integer, in the unit disk E = |z| < 1, f being regular in 0 < |z| < 1. Let $L_{n, p} (α) = f : f \in M ₚ, R e - (z^{p + 1} / p) {(D ⁿ f)}^{'} > α$ , α < 1, where $D ⁿ f = {(z^{n + p} f (z))}^{(n)} / (z^{p} n!)$ . Results on $L_{n, p} (α)$ are derived by proving more general results on differential subordination. These results reduce, by putting p =1, to the recent results of Al-Amiri and Mocanu.

Pull-back of currents by meromorphic maps

Tuyen Trung Truong (2013)

Bulletin de la Société Mathématique de France

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Let $X$ and $Y$ be compact Kähler manifolds, and let $f : X \to Y$ be a dominant meromorphic map. Based upon a regularization theorem of Dinh and Sibony for DSH currents, we define a pullback operator $f^{♯}$ for currents of bidegrees $(p, p)$ of finite order on $Y$ (and thus forcurrent, since $Y$ is compact). This operator has good properties as may be expected. Our definition and results are compatible to those of various previous works of Meo, Russakovskii and Shiffman, Alessandrini and Bassanelli, Dinh and Sibony,...

Uniqueness of $q$ -shift difference polynomials of meromorphic functions sharing a small function

Renukadevi S. Dyavanal, Rajalaxmi V. Desai (2020)

Mathematica Bohemica

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We investigate the uniqueness of a $q$ -shift difference polynomial of meromorphic functions sharing a small function which extend the results of N. V. Thin (2017) to $q$ -difference operators.

Finite logarithmic order meromorphic solutions of linear difference/differential-difference equations

Abdelkader Dahmani, Benharrat Belaidi (2025)

Mathematica Bohemica

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Firstly we study the growth of meromorphic solutions of linear difference equation of the form $A_{k} (z) f (z + c_{k}) + \dots + A_{1} (z) f (z + c_{1}) + A_{0} (z) f (z) = F (z),$ where $A_{k} (z), ..., A_{0} (z)$ and $F (z)$ are meromorphic functions of finite logarithmic order, $c_{i}$ $(i = 1, ..., k, k \in ℕ)$ are distinct nonzero complex constants. Secondly, we deal with the growth of solutions of differential-difference equation of the form $\sum_{i = 0}^{n} \sum_{j = 0}^{m} A_{i j} (z) f^{(j)} (z + c_{i}) = F (z),$ where $A_{i j} (z)$ $(i = 0, 1, ..., n, j = 0, 1, ..., m, n, m \in ℕ)$ and $F (z)$ are meromorphic functions of finite logarithmic order, $c_{i}$ $(i = 0, ..., n)$ are distinct complex constants. We extend some previous results...

Meromorphic function sharing a small function with a linear differential polynomial

Indrajit Lahiri, Amit Sarkar (2016)

Mathematica Bohemica

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The problem of uniqueness of an entire or a meromorphic function when it shares a value or a small function with its derivative became popular among the researchers after the work of Rubel and Yang (1977). Several authors extended the problem to higher order derivatives. Since a linear differential polynomial is a natural extension of a derivative, in the paper we study the uniqueness of a meromorphic function that shares one small function CM with a linear differential polynomial, and...

On the uniqueness problem for meromorphic mappings with truncated multiplicities

Feng Lü (2014)

Annales Polonici Mathematici

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The purpose of this paper is twofold. The first is to weaken or omit the condition $d i m f^{- 1} (H_{i} \cap H_{j}) \leq m - 2$ for i ≠ j in some previous uniqueness theorems for meromorphic mappings. The second is to decrease the number q of hyperplanes $H_{j}$ such that f(z) = g(z) on $⋃_{j = 1}^{q} f^{- 1} (H_{j})$ , where f,g are meromorphic mappings.

Some subclasses of meromorphic and multivalent functions

Ding-Gong Yang, Jin-Lin Liu (2014)

Annales Polonici Mathematici

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The authors introduce two new subclasses $F_{p, k} (λ, A, B)$ and $G_{p, k} (λ, A, B)$ of meromorphically multivalent functions. Distortion bounds and convolution properties for $F_{p, k} (λ, A, B)$ , $G_{p, k} (λ, A, B)$ and their subclasses with positive coefficients are obtained. Some inclusion relations for these function classes are also given.

Generalizations on the results of Cao and Zhang

Sujoy Majumder, Rajib Mandal (2022)

Mathematica Bohemica

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We establish some uniqueness results for meromorphic functions when two nonlinear differential polynomials $P (f) \prod_{i = 1}^{k} {(f^{(i)})}^{n_{i}}$ and $P (g) \prod_{i = 1}^{k} {(g^{(i)})}^{n_{i}}$ share a nonzero polynomial with certain degree and our results improve and generalize some recent results in Y.-H. Cao, X.-B. Zhang (2012). Also we exhibit two examples to show that the conditions used in the results are sharp.

On the meromorphic solutions of a certain type of nonlinear difference-differential equation

Sujoy Majumder, Lata Mahato (2023)

Mathematica Bohemica

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The main objective of this paper is to give the specific forms of the meromorphic solutions of the nonlinear difference-differential equation $f^{n} (z) + P_{d} (z, f) = p_{1} (z) e^{α_{1} (z)} + p_{2} (z) e^{α_{2} (z)},$ where $P_{d} (z, f)$ is a difference-differential polynomial in $f (z)$ of degree $d \leq n - 1$ with small functions of $f (z)$ as its coefficients, $p_{1}$ , $p_{2}$ are nonzero rational functions and $α_{1}$ , $α_{2}$ are non-constant polynomials. More precisely, we find out the conditions for ensuring the existence of meromorphic solutions of the above equation.

Nonlinear differential monomials sharing two values

Sujoy Majumder (2016)

Mathematica Bohemica

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Using the notion of weighted sharing of values which was introduced by Lahiri (2001), we deal with the uniqueness problem for meromorphic functions when two certain types of nonlinear differential monomials namely $h^{n} h^{(k)}$ $(h = f, g)$ sharing a nonzero polynomial of degree less than or equal to $3$ with finite weight have common poles and obtain two results. The results in this paper significantly rectify, improve and generalize the results due to Cao and Zhang (2012).

Uniqueness results for differential polynomials sharing a set

Soniya Sultana, Pulak Sahoo (2025)

Mathematica Bohemica

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We investigate the uniqueness results of meromorphic functions if differential polynomials of the form ${(Q (f))}^{(k)}$ and ${(Q (g))}^{(k)}$ share a set counting multiplicities or ignoring multiplicities, where $Q$ is a polynomial of one variable. We give suitable conditions on the degree of $Q$ and on the number of zeros and the multiplicities of the zeros of $Q^{'}$ . The results of the paper generalize some results due to T. T. H. An and N. V. Phuong (2017) and that of N. V. Phuong (2021).

On the generalization of two results of Cao and Zhang

Sujoy Majumder (2017)

Mathematica Bohemica

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This paper studies the uniqueness of meromorphic functions $f^{n} \prod_{i = 1}^{k} {(f^{(i)})}^{n_{i}} and g^{n} \prod_{i = 1}^{k} {(g^{(i)})}^{n_{i}}$ that share two values, where $n, n_{k}, k \in ℕ$ , $n_{i} \in ℕ \cup {0}$ , $i = 1, 2, ..., k - 1$ . The results significantly rectify, improve and generalize the results due to Cao and Zhang (2012).

On meromorphic functions defined by a differential system of order $1$

Tristan Torrelli (2004)

Bulletin de la Société Mathématique de France

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Given a germ $h$ of holomorphic function on $(ℂ^{n}, 0)$ , we study the condition: “the ideal ${Ann}_{𝒟} 1 / h$ is generated by operators of order1”. We obtain here full characterizations in the particular cases of Koszul-free germs and unreduced germs of plane curves. Moreover, we prove that this condition holds for a special type of hyperplane arrangements. These results allow us to link this condition to the comparison of de Rham complexes associated with $h$ .

Uniqueness and differential polynomials of meromorphic functions sharing a nonzero polynomial

Pulak Sahoo (2016)

Mathematica Bohemica

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Let $k$ be a nonnegative integer or infinity. For $a \in ℂ \cup {\infty}$ we denote by $E_{k} (a; f)$ the set of all $a$ -points of $f$ where an $a$ -point of multiplicity $m$ is counted $m$ times if $m \leq k$ and $k + 1$ times if $m > k$ . If $E_{k} (a; f) = E_{k} (a; g)$ then we say that $f$ and $g$ share the value $a$ with weight $k$ . Using this idea of sharing values we study the uniqueness of meromorphic functions whose certain nonlinear differential polynomials share a nonzero polynomial with finite weight. The results of the paper improve and generalize the related results due to...

Twists and resonance of $L$ -functions, I

Jerzy Kaczorowski, Alberto Perelli (2016)

Journal of the European Mathematical Society

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We obtain the basic analytic properties, i.e. meromorphic continuation, polar structure and bounds for the order of growth, of all the nonlinear twists with exponents $\leq 1 / d$ of the $L$ -functions of any degree $d \geq 1$ in the extended Selberg class. In particular, this solves the resonance problem in all such cases.

Distribution of zeros and shared values of difference operators

Jilong Zhang, Zongsheng Gao, Sheng Li (2011)

Annales Polonici Mathematici

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We investigate the distribution of zeros and shared values of the difference operator on meromorphic functions. In particular, we show that if f is a transcendental meromorphic function of finite order with a small number of poles, c is a non-zero complex constant such that $Δ_{c}^{k} f \neq 0$ for n ≥ 2, and a is a small function with respect to f, then $f ⁿ Δ_{c}^{k} f$ equals a (≠ 0,∞) at infinitely many points. Uniqueness of difference polynomials with the same 1-points or fixed points is also proved.

Maximally convergent rational approximants of meromorphic functions

Hans-Peter Blatt (2015)

Banach Center Publications

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Let f be meromorphic on the compact set E ⊂ C with maximal Green domain of meromorphy $E_{ρ (f)}$ , ρ(f) < ∞. We investigate rational approximants $r_{n, m ₙ}$ of f on E with numerator degree ≤ n and denominator degree ≤ mₙ. We show that a geometric convergence rate of order $ρ {(f)}^{- n}$ on E implies uniform maximal convergence in m₁-measure inside $E_{ρ (f)}$ if mₙ = o(n/log n) as n → ∞. If mₙ = o(n), n → ∞, then maximal convergence in capacity inside $E_{ρ (f)}$ can be proved at least for a subsequence Λ ⊂ ℕ. Moreover, an analogue...

Uniqueness of entire functions and fixed points

Xiao-Guang Qi, Lian-Zhong Yang (2010)

Annales Polonici Mathematici

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Let f and g be entire functions, n, k and m be positive integers, and λ, μ be complex numbers with |λ| + |μ| ≠ 0. We prove that ${(f ⁿ (z) (λ f^{m} (z) + μ))}^{(} k)$ must have infinitely many fixed points if n ≥ k + 2; furthermore, if ${(f ⁿ (z) (λ f^{m} (z) + μ))}^{(} k)$ and ${(g ⁿ (z) (λ g^{m} (z) + μ))}^{(} k)$ have the same fixed points with the same multiplicities, then either f ≡ cg for a constant c, or f and g assume certain forms provided that n > 2k + m* + 4, where m* is an integer that depends only on λ.