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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 Openarrow_drop_down
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Asymptotic series and algebroid functions

Authors: Levin, B. Ya.; Ronkin, A. L.;

Asymptotic series and algebroid functions

Abstract

The main result of this very saturated note is the following theorem. Let the coefficients \(P_{\ell}(z)\) of the equation \[ (1)\quad P_ 0(z)w^ n+P_ 1(z)w^{n-1}+...+P_ n(z)=0 \] admit in an angle \(S_{\beta}\equiv S_{0,\beta}\), \(S_{\phi,\beta}=\{z:\) \(| \arg z- \phi | \pi)\) and let the set \(\{\lambda_{j\ell}\}\) be separated. Then for some \(\alpha <\beta\) the branches of the solution of (1) in \(S_{\alpha}\) admit each on its own Riemann surface asymptotic expansions \[ w_ k(z)\sim \sum^{r_ k}_{p=0}d_{kp}(z)\exp \{- \mu_ pz\},\quad k=1,...,n,\quad r_ k<\infty, \] where exponents \(\mu_ p\) are represented over \(\lambda_{j\ell}\) and \(d_{kp}\) are meromorphic functions of degree zero. As consequence the authors received the following generalization of the Ritt theorems. If the entire function \(w=w(z)\) satisfies to (1) with \[ P_ j(z)=\sum^{\mu_ j}_{k=0}c_{j\ell}(z)e^{- \lambda_{j\ell}z}, \] \(c_{j\ell}\) are polynomials, then \(w=[Q(z)]^{-1}f(z)\), where Q is a polynomial, and f is a P-quasi- polynomial with special indices.

Keywords

Asymptotic representations in the complex plane, Ritt theorems, meromorphic functions, algebroidal function, Functional equations in the complex plane, iteration and composition of analytic functions of one complex variable, quasi- polynomial, Entire and meromorphic functions of one complex variable, and related topics

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