On the interpolation in some classes of holomorphic in the unit disk functions

There is considered an interpolation problem $f(\lambda_n )=b_n$ in the class of holomorphic in the unit disk $U(0;1)=\{z\in\mathbb{C}\colon |z|<1\}$functions of finite $\eta$-type, i.e such that $\displaystyle (\exists A>0)(\forall z\in U(0;1))\colon \quad |f(z)|\leq\exp\Big(A\eta\Big(\frac A{1-|z|}\Big)\Big),$ where $\eta\colon [1;+\infty)\to [0;+\infty)$ is an increasing convex function with respect to $\ln{t}$ and $\ln{t}=o\left(\eta ( t)\right)$ $(t\to+\infty)$.There were received sufficient conditions of the interpolation problem solvability in terms of the counting functions $\displaystyle N(r)=\int\nolimits_{0}^{r}\frac{\left(n(t)-1\right)^+}{t}dt$ and $\displaystyle N_{\lambda_n} (r)=\int\nolimits_{0}^{r}{\frac{{{(n}_{\lambda_n}\left(t\right)-1)}^+}{t}dt}$. Earlier, in 2004, necessary conditions were obtained (Ukr. Math. J., {\bf 56} (2004), \No 3) in these terms.For the moderate growth of $f$ (when the majorant $\eta=\psi$ satisfies the condition $\psi\left(2x\right)=O\left(\psi\left(x\right)\right),\ x\rightarrow+\infty$) that problem was solved in J. Math. Anal. Appl., {\bf 414} (2014), \No 1.In this paper, we remove any restrictions on the growth of $\eta$ and construct an interpolation function $f$ such that$\displaystyle (\exists A'>0)(\forall z\in U(0;1))\colon \quad |{f}(z)|\leq\exp\Big(\frac{A'}{(1-|z|)^{3/2}}\eta\Big(\frac{A'}{1-|z|}\Big)\Big)$.

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Publication Details

Journal
Matematychni Studii
Published
2024-09-15
DOI
https://doi.org/10.30970/ms.62.1.31-38
Primary Topic
Analytic and geometric function theory
Type
article
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On the interpolation in some classes of holomorphic in the unit disk functions

Iryna Sheparovych
Matematychni Studii
Analytic and geometric function theory
article

On the interpolation in some classes of holomorphic in the unit disk functions

Iryna Sheparovych
article en

Abstract

There is considered an interpolation problem $f(\lambda_n )=b_n$ in the class of holomorphic in the unit disk $U(0;1)=\{z\in\mathbb{C}\colon |z|<1\}$functions of finite $\eta$-type, i.e such that $\displaystyle (\exists A>0)(\forall z\in U(0;1))\colon \quad |f(z)|\leq\exp\Big(A\eta\Big(\frac A{1-|z|}\Big)\Big),$ where $\eta\colon [1;+\infty)\to [0;+\infty)$ is an increasing convex function with respect to $\ln{t}$ and $\ln{t}=o\left(\eta ( t)\right)$ $(t\to+\infty)$.There were received sufficient conditions of the interpolation problem solvability in terms of the counting functions $\displaystyle N(r)=\int\nolimits_{0}^{r}\frac{\left(n(t)-1\right)^+}{t}dt$ and $\displaystyle N_{\lambda_n} (r)=\int\nolimits_{0}^{r}{\frac{{{(n}_{\lambda_n}\left(t\right)-1)}^+}{t}dt}$. Earlier, in 2004, necessary conditions were obtained (Ukr. Math. J., {\bf 56} (2004), \No 3) in these terms.For the moderate growth of $f$ (when the majorant $\eta=\psi$ satisfies the condition $\psi\left(2x\right)=O\left(\psi\left(x\right)\right),\ x\rightarrow+\infty$) that problem was solved in J. Math. Anal. Appl., {\bf 414} (2014), \No 1.In this paper, we remove any restrictions on the growth of $\eta$ and construct an interpolation function $f$ such that$\displaystyle (\exists A'>0)(\forall z\in U(0;1))\colon \quad |{f}(z)|\leq\exp\Big(\frac{A'}{(1-|z|)^{3/2}}\eta\Big(\frac{A'}{1-|z|}\Big)\Big)$.

Matematychni StudiiVol. 62(1)
Drohobych Ivan Franko State Pedagogical University (UA)
Openalex Percentile: Top 75%
Analytic and geometric function theory
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