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The support of a function with thin spectrum

Kathryn Hare (1994)

Colloquium Mathematicae

We prove that if E Ĝ does not contain parallelepipeds of arbitrarily large dimension then for any open, non-empty S G there exists a constant c > 0 such that f 1 S 2 c f 2 for all f L 2 ( G ) whose Fourier transform is supported on E. In particular, such functions cannot vanish on any open, non-empty subset of G. Examples of sets which do not contain parallelepipeds of arbitrarily large dimension include all Λ(p) sets.

The theory of reproducing systems on locally compact abelian groups

Gitta Kutyniok, Demetrio Labate (2006)

Colloquium Mathematicae

A reproducing system is a countable collection of functions ϕ j : j such that a general function f can be decomposed as f = j c j ( f ) ϕ j , with some control on the analyzing coefficients c j ( f ) . Several such systems have been introduced very successfully in mathematics and its applications. We present a unified viewpoint in the study of reproducing systems on locally compact abelian groups G. This approach gives a novel characterization of the Parseval frame generators for a very general class of reproducing systems on L²(G)....

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