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Proceedings of the American Mathematical Society
Article . 1987 . Peer-reviewed
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Proceedings of the American Mathematical Society
Article . 1987 . Peer-reviewed
Data sources: Crossref
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Some New Multipliers of Fourier Series

Some new multipliers of Fourier series
Authors: Buntinas, Martin;

Some New Multipliers of Fourier Series

Abstract

Let L 1 {L^1} be the space of all complex-valued 2 π 2\pi -periodic integrable functions f f and let L 1 ^ \widehat {{L^1}} be the space of sequences of Fourier coefficients f ^ \hat f . A sequence λ \lambda is an ( L 1 ^ → L 1 ^ ) \left ( {\widehat {{L^1}} \to \widehat {{L^1}}} \right ) multiplier if λ ⋅ f ^ = ( λ ( n ) f ^ ( n ) ) \lambda \cdot \hat f = \left ( {\lambda \left ( n \right )\hat f\left ( n \right )} \right ) belongs to L 1 ^ \widehat {{L^1}} for every f f in L 1 {L^1} . The space of even sequences of bounded variation is defined by b υ = { λ | λ n = λ − n , ∑ k = 0 ∞ | Δ λ k | + sup n | λ n | > ∞ } b\upsilon = \left \{ {\lambda \left | {{\lambda _n} = {\lambda _{ - n}},\sum \nolimits _{k = 0}^\infty {\left | {\Delta {\lambda _k}} \right |} + {{\sup }_n}\left | {{\lambda _n}} \right | > \infty } \right .} \right \} , where Δ λ k = λ k − λ k + 1 \Delta {\lambda _k} = {\lambda _k} - {\lambda _{k + 1}} and the space of even bounded quasiconvex sequences is defined by q = { λ | λ n = λ − n , ∑ k = 1 ∞ k | Δ 2 λ k | + sup n | λ n | > ∞ } q = \left \{ {\lambda \left | {{\lambda _n} = {\lambda _{ - n}},\sum \nolimits _{k = 1}^\infty {k\left | {{\Delta ^2}{\lambda _k}} \right | + {{\sup }_n}\left | {{\lambda _n}} \right | > \infty } } \right .} \right \} , where Δ 2 λ k = Δ λ k − Δ λ k + 1 {\Delta ^2}{\lambda _k} = \Delta {\lambda _k} - \Delta {\lambda _{k + 1}} . It is well known that q ⊂ b υ q \subset b\upsilon and q ⊂ ( L 1 ^ → L 1 ^ ) q \subset \left ( {\widehat {{L^1}} \to \widehat {{L^1}}} \right ) but b υ ⊄ ( L 1 ^ → L 1 ^ ) b\upsilon \not \subset \left ( {\widehat {{L^1}} \to \widehat {{L^1}}} \right ) . This result is significantly improved by finding an increasing family of sequence spaces d υ p d{\upsilon _p} between q q and b υ b\upsilon which are ( L 1 ^ → L 1 ^ ) \left ( {\widehat {{L^1}} \to \widehat {{L^1}}} \right ) multipliers. Since the ( L 1 ^ → L 1 ^ ) \left ( {\widehat {{L^1}} \to \widehat {{L^1}}} \right ) multipliers are the 2 π 2\pi -periodic measures, this result gives sufficient conditions for a sequence to be the Fourier coefficients of a measure.

Keywords

Fourier coefficients, Fourier series of functions with special properties, special Fourier series, Convolution, factorization for one variable harmonic analysis, multipliers, Fourier coefficients, sequence spaces, Multipliers in one variable harmonic analysis

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selected citations
These citations are derived from selected sources.
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
4
Average
Top 10%
Average
bronze