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JOURNALS // Matematicheskii Sbornik // Archive

Mat. Sb. (N.S.), 1984 Volume 125(167), Number 2(10), Pages 181–198 (Mi sm2078)

This article is cited in 11 papers

On separation of singularities of meromorphic functions

V. I. Danchenko


Abstract: Let $E$ be an arbitrary bounded proper continuum on $\overline{\mathbf C}$, $\lambda$ a finite collection of pairwise distinct domains that are components of $\overline{\mathbf C}\setminus E$, $f$ a function meromorphic in each domain $G\in\lambda$ and continuous in some neighborhood of $E$, $f_\lambda$ the sum of the principal parts of the Laurent expansions of $f$ with respect to its poles in the union of the domains in $\lambda$, and $n_\lambda$ the degree of the rational function $f_\lambda$. If all the domains $G\in\lambda$ are bounded, then $\|f_\lambda\|_{C(E)}\leqslant\mathrm{const}\cdot n_\lambda\|f\|_{C(E)}$. If $E$ is a rectifiable curve $\Gamma$, then the total variation $\operatorname{Var}(f_\lambda,\Gamma)=\int_\Gamma|f_\lambda'(\zeta)|\cdot|d\zeta|$ of $f_\lambda$ along $\Gamma$ satisfies $\operatorname{Var}(f_\lambda,\Gamma)\leqslant\mathrm{const}\cdot n_\lambda\ln^3(en_\lambda)\|f\|_{C(\Gamma)}V(\Gamma)$, where $V(\Gamma)$ is the supremum of the set $\{\operatorname{Var}(r,\Gamma)\}$ of total variations along $\Gamma$ of all the partial fractions $r(z)=a/(bz+c)$ with $\|r\|_{C(\Gamma)}=1$.
Bibliography: 11 titles.

UDC: 517.53

MSC: 30A10, 30C99, 30D30

Received: 19.09.1983


 English version:
Mathematics of the USSR-Sbornik, 1986, 53:1, 183–201

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