Beurling algebra

In mathematics, the term Beurling algebra is used for different algebras introduced by Arne Beurling (1949), usually it is an algebra of periodic functions with Fourier series

f(x)=\sum a_{n}e^{inx}

Example We may consider the algebra of those functions f where the majorants

c_{k}=\sup _{|n|\geq k}|a_{n}|

of the Fourier coefficients a_n are summable. In other words

\sum _{k\geq 0}c_{k}<\infty .

Example We may consider a weight function w on $\mathbb {Z}$ such that

w(m+n)\leq w(m)w(n),\quad w(0)=1

in which case $A_{w}(\mathbb {T} )=\{f:f(t)=\sum _{n}a_{n}e^{int},\,\|f\|_{w}=\sum _{n}|a_{n}|w(n)<\infty \}\,(\sim \ell _{w}^{1}(\mathbb {Z} ))$ is a unitary commutative Banach algebra.

These algebras are closely related to the Wiener algebra.

References

Belinsky, E.S.; Liflyand, E.R. (2001), "B/b130120", in Hazewinkel, Michiel, Encyclopedia of Mathematics, Springer, ISBN 978-1-55608-010-4
Beurling, Arne (1949), "On the spectral synthesis of bounded functions", Acta Math., 81 (1): 225–238, doi:10.1007/BF02395018, MR 0027891

This article is issued from Wikipedia - version of the 8/19/2014. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.