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Hausdorff and quasi-Hausdorff matrices on spaces of analytic functions. (English) Zbl 1105.47029

Let \(\mu\) be a finite positive measure on the real interval \((0,1)\), for \(1\leq p<\infty\), let \(H^p\) denote the Hardy space of analytic functions on the unit disc \(\mathbb{D}= \{z\in\mathbb{C}:|z|< 1\}\), and let \(A^p\) denote the Bergman space on \(\mathbb{D}\).
An infinite lower triangular Hausdorff matrix \(H= \{c_{n,k}\}\) has entries \(c_{n,k}\) defined by \(c_{n,k}= {^nC_k}\int^1_0 t^k(1- t)^{n-k} d\mu(t)\), with \({^nC_k}= n!/((n- k)!k!)\), \(k= 0,1,2,\dots, n\). If \((X,\|.\|_X)\) is a Banach space of analytic functions on \(\mathbb{D}\) with norm \(\|.\|_X\) and if \(f\in X\) has the representation \(f(z)= \sum^\infty_{n=0} a_n z^n\), then the transform \({\mathcal H}_\mu(f)\) and transpose operator \({\mathcal A}_\mu\) are defined formally as \[ {\mathcal H}_\mu(f)(z)= \sum^\infty_{n= 0}\,\Biggl(\sum^n_{k=0} c_{n,k}a_k\Biggr) z^n;\;{\mathcal A}_\mu(f)(z)= \sum^\infty_{k= 0}\,\Biggl(\sum^\infty_{n=k} c_{n,k} a_n\Biggr)z^n. \] In addition, the operators \({\mathcal S}_\mu\), \({\mathcal T}_\mu\) are defined by \[ {\mathcal S}_\mu(f)(z)= \int^1_0 w_t(z) f(\varphi_t(z))\,d\mu(t);\;{\mathcal T}_\mu(f)(z)= \int^1_0 f(\psi_t(z))\,d\mu(t), \] where \(\varphi_t(z)= tz/((t- 1)z+ 1)\), \(\psi_t(z)= zt+ 1-t\); \(w_t(z)= ((t- 1)z+ 1)- 1\), \(z\in\mathbb{D}\).
The main results of this paper provide necessary and sufficient conditions so that
(i) \({\mathcal H}_\mu={\mathcal S}_\mu: H^p\to H^p\) or (ii) \({\mathcal H}_\mu={\mathcal S}_\mu: A^p\to A^p\) is a bounded operator;
(iii) \({\mathcal A}_\mu: H^p\to H^p\) or (iv) \({\mathcal A}_\mu: A^p\to A^p\) is a bounded operator.
In particular, in case (i), the applicable conditions include \(\int^1_0 t^{(1/p)-1}d\mu(t)< \infty\) and in the cases (ii), (iii), (iv), the applicable conditions include \(\int^1_0 t^{-\delta/p} d\mu(t)< \infty\), \(\delta= 1\) or \(2\). It is also shown that \({\mathcal A}_\mu\) in \(H^{p'}\) is the adjoint of \({\mathcal H}_\mu\) in \(H^p\), where \((1/p)+ (1/p')= 1\).
The introduction of the paper contains statements that earlier papers, including [P. Galanopoulos and A. Siskakis, Ill.J.Math.45, No. 3, 757–773 (2001; Zbl 0994.47026)] and O. Rudolf [“Hausdorff–Operatoren auf BK-Räumen und Halbgruppen linearer Operatoren” (Mitteillungen aus dem Mathematischen Seminar Gießen 241) (Diss. Univ. Gießen) (2000; Zbl 1104.47302)] contain results which indicate sufficient conditions for (i) in the case \(2\leq p<\infty\), and state different proofs for the results (i) and (iv).

MSC:

47B38 Linear operators on function spaces (general)
46E15 Banach spaces of continuous, differentiable or analytic functions
40G05 Cesàro, Euler, Nörlund and Hausdorff methods
42A20 Convergence and absolute convergence of Fourier and trigonometric series
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