Abstract
We consider a Hilbert space H equipped with a set of strongly continuous bounded semigroups satisfying certain conditions. The conditions allow to define a family of moduli of continuity Ωr(s, f), r ∈ ℕ, s > 0, of vectors in H and a family of Paley—Wiener subspaces PWσ parametrized by bandwidth σ > 0. These subspaces are explored to introduce notion of the best approximation ε(σ, f) of a general vectorin H by Paley—Wiener vectors of a certain bandwidth σ > 0. The main objective of the paper is to prove the so-called Jackson-type estimate ε(σ, f) ≤ C(Ωr(σ−1, f)+σ−r ∥f∥) for σ > 1. Our assumptions are satisfied for a strongly continuous unitary representation of a Lie group G in a Hilbert space H. It allows to obtain the Jackson-type estimates on homogeneous manifolds.
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Pesenson, I.Z. Jackson-Type Inequality in Hilbert Spaces and on Homogeneous Manifolds. Anal Math 48, 1153–1168 (2022). https://doi.org/10.1007/s10476-022-0176-0
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DOI: https://doi.org/10.1007/s10476-022-0176-0
Key words and phrases
- Jackson-type inequality
- K-functor
- one-parameter group of operators
- Paley—Wiener vector
- modulus of continuity
- nitary representation of Lie groups
- homogeneous manifold