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Journal of the Belarusian State University. Mathematics and Informatics, 2018, Volume 1, Pages 10–16 (Mi bgumi125)  

Real, Complex and Functional analysis

Integrate inequalities for the higher derivatives of Blashke product

T. S. Mardvilko

Belarusian State University, 4 Niezaliežnasci avenue, Minsk 220030, Belarus
References:
Abstract: Upper and lower inequalities for the higher derivatives of Blashke product in the Lebesgue space $L_{p}$ are obtained in this work. All $p\in (0,+\infty)\setminus \{\frac{1}{s}\}, s\in \mathbb{N}\setminus \{1\}$, are considered, where s is order of the derivative. The case $p = \frac{1}{s}$ was investigated by the author earlier.
Let $a_{n}=\{a_{1},\dots , a_{n}\}$ be a certain set of $n$ complex numbers laying in the unit disc $|z| < 1$. Let us introduce the Blashke products $b_{n}(z)=\displaystyle\prod_{k=1}^{n} \frac{z-a_{k}}{1-\bar{a_{k}}z}$ with zeros at the points $a_{1}, a_{2},\dots , a_{n}$.
For $0<p<\frac{1}{s}$ and $s\in \mathbb{N}$ holds the equality $\displaystyle\inf_{a_{n}}\lVert b_{n}^{(s)}\rVert_{L_{p}}=0$. For $p>1$ $\displaystyle\inf_{a_{n}}\lVert b_{n}^{'}\rVert_{L_{p}}=n$. For $\frac{1}{s}<p<\infty$ and $s\in \mathbb{N}$ holds the equality $\displaystyle\sup_{a_{n}}\lVert b_{n}^{(s)}\rVert_{L_{p}}=+\infty$. In other cases, the obtained estimates are exact in order. The main results of the present paper are stated in theorems $1 - 5$.
Keywords: Blashke product; rational functions; higher derivatives; Lebesgue space.
Funding agency Grant number
Государственная программа научных исследований Республики Беларусь «Конвергенция»
This work supported by state programs for scientific research of the National Academy of Sciences of Belarus «Convergence».
Received: 28.09.2017
Document Type: Article
UDC: 517.51+517.53
Language: Russian
Citation: T. S. Mardvilko, “Integrate inequalities for the higher derivatives of Blashke product”, Journal of the Belarusian State University. Mathematics and Informatics, 1 (2018), 10–16
Citation in format AMSBIB
\Bibitem{Mar18}
\by T.~S.~Mardvilko
\paper Integrate inequalities for the higher derivatives of Blashke product
\jour Journal of the Belarusian State University. Mathematics and Informatics
\yr 2018
\vol 1
\pages 10--16
\mathnet{http://mi.mathnet.ru/bgumi125}
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