## Cesàro averaging operators.(English)Zbl 1024.47014

K. F. Andersen proved in [Proc. R. Soc. Edinb., Sect. A 126, 617-624 (1996; Zbl 0865.47020)] that the generalized Cesàro operator defined by $C^{\gamma} f(z)= \sum_{n=0}^\infty \bigg({1\over A_n^{\gamma+1}}\sum_{k=0}^n A_{n-k}^{\gamma}a_k\bigg) z^n,$ where $$f(z)=\sum_{n=0}^\infty a_n z^n$$ is an analytic function on the unit disc $$U$$ and $$A_k^\gamma$$ is the $$k$$th coefficient of the series expansion satisfying of $$(1-x)^{-1-\gamma}$$, satisfies the following inequality $M_p( C^{\gamma} f, r)\leq C_{\gamma, p} M_p( f, r)$ for every $$0<r<1$$ and Re $$\gamma>-1$$, where $$M_p$$ denotes the integral mean in $$L^p$$. In the present paper, the above result is extended to analytic functions defined in the polydisk where the operator $$C^{\gamma}$$ is substituted by the so-called generalized Cesàro operator $C^{\bar\gamma} f(z)= \sum_{|\alpha|=0} \Biggl({\sum_{\beta\leq\alpha} (\prod_{j=1}^n A_{\beta_j}^{\gamma_j}) a_{ \alpha-\beta } \over \prod_{j=1}^n A_{\alpha_j}^{\gamma_j+1}} \Biggr) z^\alpha,$ whenever $$f(z)=\sum_{|\alpha|=0}^\infty a_\alpha z^\alpha$$ is an analytic function on $$U^n$$.

### MSC:

 47B38 Linear operators on function spaces (general) 46E15 Banach spaces of continuous, differentiable or analytic functions 30H05 Spaces of bounded analytic functions of one complex variable

Zbl 0865.47020
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