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The Cesàro and related operators, a survey

V. G. Miller (2007)

Banach Center Publications

We provide a survey of properties of the Cesàro operator on Hardy and weighted Bergman spaces, along with its connections to semigroups of weighted composition operators. We also describe recent developments regarding Cesàro-like operators and indicate some open questions and directions of future research.

The group of L²-isometries on H¹₀

Esteban Andruchow, Eduardo Chiumiento, Gabriel Larotonda (2013)

Studia Mathematica

Let Ω be an open subset of ℝⁿ. Let L² = L²(Ω,dx) and H¹₀ = H¹₀(Ω) be the standard Lebesgue and Sobolev spaces of complex-valued functions. The aim of this paper is to study the group of invertible operators on H¹₀ which preserve the L²-inner product. When Ω is bounded and ∂Ω is smooth, this group acts as the intertwiner of the H¹₀ solutions of the non-homogeneous Helmholtz equation u - Δu = f, u | Ω = 0 . We show that is a real Banach-Lie group, whose Lie algebra is (i times) the space of symmetrizable operators....

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