Hp spaces and integral operators
(1987) In Mathematica (Cluj) 29(52)(2). p.99-104- Abstract
- Let $\scr H(U)$ denote the class of analytic functions in the unit disc $U$ and $g$ be analytic in $U$, normalized by $g(0)=g'(0)-1=0$ and $g(z)\ne0$ for $z\in U\sbs\{0\}$. $H^p$, $0<p\le \infty$, denotes the Hardy class and $H\,\roman{log}^+\,H$ the class for which $\int_0^{2\pi}|f(re^{i\theta})| \roman{log}^+|f(re^{i\theta})|\,d\theta$ is bounded when $r\rightarrow 1^-$. The author considers the integral operator $L_g\colon \scr H(U)\rightarrow \scr H(U)$ defined by $L_g(f)(z)=(z/g(z))\int_0^{z}f(t)g'(t)\,dt$ and shows that: (i) if $zg'/g\in H\,\roman{log}^+\,H$ and $f\in H^p$ then $L_g(f)\in H^p$; (ii) if $zg'/g\in H^q$, $q>1$ and $f\in H^p$ then $L_g(f)\in H^r$ where $r=pq/(p+q-pq)$ for $0<p<q/(q-1)$ and $r=\infty$ for... (More)
- Let $\scr H(U)$ denote the class of analytic functions in the unit disc $U$ and $g$ be analytic in $U$, normalized by $g(0)=g'(0)-1=0$ and $g(z)\ne0$ for $z\in U\sbs\{0\}$. $H^p$, $0<p\le \infty$, denotes the Hardy class and $H\,\roman{log}^+\,H$ the class for which $\int_0^{2\pi}|f(re^{i\theta})| \roman{log}^+|f(re^{i\theta})|\,d\theta$ is bounded when $r\rightarrow 1^-$. The author considers the integral operator $L_g\colon \scr H(U)\rightarrow \scr H(U)$ defined by $L_g(f)(z)=(z/g(z))\int_0^{z}f(t)g'(t)\,dt$ and shows that: (i) if $zg'/g\in H\,\roman{log}^+\,H$ and $f\in H^p$ then $L_g(f)\in H^p$; (ii) if $zg'/g\in H^q$, $q>1$ and $f\in H^p$ then $L_g(f)\in H^r$ where $r=pq/(p+q-pq)$ for $0<p<q/(q-1)$ and $r=\infty$ for $p\ge\break q/(q-1)$; and (iii) if $zg'/g\in H^\infty$ and $f\in H^p$, then $L_g(f)$ is in $H^r$ where $r=p/(1-p)$ for $0<p<1$ and $r=\infty$ for $p\ge 1$. This result generalizes a result of the reviewer [same journal 29(52) (1987), no. 1, 29--31; MR0939548 (89e:30061)]. An interesting example is given. (Less)
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- author
- Aleman, Alexandru LU
- publishing date
- 1987
- type
- Contribution to journal
- publication status
- published
- subject
- in
- Mathematica (Cluj)
- volume
- 29(52)
- issue
- 2
- pages
- 99 - 104
- publisher
- Editions de l'Academie Roumaine
- ISSN
- 1222-9016
- language
- English
- LU publication?
- no
- id
- fa48100a-8c98-4515-82a7-b8d88acb3c3f (old id 1467384)
- date added to LUP
- 2016-04-04 09:24:43
- date last changed
- 2018-11-21 20:52:54
@article{fa48100a-8c98-4515-82a7-b8d88acb3c3f, abstract = {{Let $\scr H(U)$ denote the class of analytic functions in the unit disc $U$ and $g$ be analytic in $U$, normalized by $g(0)=g'(0)-1=0$ and $g(z)\ne0$ for $z\in U\sbs\{0\}$. $H^p$, $0<p\le \infty$, denotes the Hardy class and $H\,\roman{log}^+\,H$ the class for which $\int_0^{2\pi}|f(re^{i\theta})| \roman{log}^+|f(re^{i\theta})|\,d\theta$ is bounded when $r\rightarrow 1^-$. The author considers the integral operator $L_g\colon \scr H(U)\rightarrow \scr H(U)$ defined by $L_g(f)(z)=(z/g(z))\int_0^{z}f(t)g'(t)\,dt$ and shows that: (i) if $zg'/g\in H\,\roman{log}^+\,H$ and $f\in H^p$ then $L_g(f)\in H^p$; (ii) if $zg'/g\in H^q$, $q>1$ and $f\in H^p$ then $L_g(f)\in H^r$ where $r=pq/(p+q-pq)$ for $0<p<q/(q-1)$ and $r=\infty$ for $p\ge\break q/(q-1)$; and (iii) if $zg'/g\in H^\infty$ and $f\in H^p$, then $L_g(f)$ is in $H^r$ where $r=p/(1-p)$ for $0<p<1$ and $r=\infty$ for $p\ge 1$. This result generalizes a result of the reviewer [same journal 29(52) (1987), no. 1, 29--31; MR0939548 (89e:30061)]. An interesting example is given.}}, author = {{Aleman, Alexandru}}, issn = {{1222-9016}}, language = {{eng}}, number = {{2}}, pages = {{99--104}}, publisher = {{Editions de l'Academie Roumaine}}, series = {{Mathematica (Cluj)}}, title = {{Hp spaces and integral operators}}, volume = {{29(52)}}, year = {{1987}}, }