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This article is cited in 20 scientific papers (total in 20 papers)
Estimates of the distances from the poles of logarithmic derivatives of polynomials to lines and circles
V. I. Danchenko
Abstract:
Estimates are obtained for the distances $d(Q,\Gamma)$ from poles of the logarithmic derivative $\theta_Q=Q'/Q$ of a polynomial $Q$ to lines $\Gamma$ of the extended complex plane in dependence on the degree $\deg Q$ of the polynomial $Q$ and the norm of
$\theta_Q$ in a certain metric on $\Gamma$. The smallest deviations are defined to be
$$
d_n(\Gamma )=\inf \{d(Q,\Gamma ):\|\theta _Q\|_{C(\Gamma )}\leqslant 1,
\deg Q\le n\},\qquad n=1,2,\dotsc .
$$
In this case if $\Gamma_1$ is the real axis, then $d_n(\Gamma_1)\asymp\ln\ln n/\ln n$, and if $\Gamma_2$ is the unit circle $\vert z\vert=1$, then $d_n(\Gamma_2)\asymp\ln n/n$. When the derivative $\theta'_Q$ is normalized in the metric of $C(\Gamma_1)$, $d_n'(\Gamma_1)\asymp\ln n/\sqrt{n}$ for the corresponding smallest deviation. When
$\theta_Q$ is normalized in the metric of $L_p(\Gamma_1)$, $1<p<\infty$, the corresponding smallest deviations do not decrease to zero as $n$ increases, and are bounded below by the quantity $1/p(\sin\pi/p)^{p/(p-1)}$.
Received: 28.09.1993
Citation:
V. I. Danchenko, “Estimates of the distances from the poles of logarithmic derivatives of polynomials to lines and circles”, Russian Acad. Sci. Sb. Math., 82:2 (1995), 425–440
Linking options:
https://www.mathnet.ru/eng/sm918https://doi.org/10.1070/SM1995v082n02ABEH003573 https://www.mathnet.ru/eng/sm/v185/i8/p63
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Abstract page: | 559 | Russian version PDF: | 197 | English version PDF: | 10 | References: | 79 | First page: | 1 |
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