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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