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Wiener Algebras and Trigonometric Series in a Coordinated Fashion
Constructive Approximation ( IF 2.3 ) Pub Date : 2021-03-10 , DOI: 10.1007/s00365-021-09527-4
E. Liflyand , R. Trigub

Let \(W_0(\mathbb {R})\) be the Wiener Banach algebra of functions representable by the Fourier integrals of Lebesgue integrable functions. It is proved in the paper that, in particular, a trigonometric series \(\sum \nolimits _{k=-\infty }^\infty c_k e^{ikt}\) is the Fourier series of an integrable function if and only if there exists a \(\phi \in W_0(\mathbb {R})\) such that \(\phi (k)=c_k\), \(k\in \mathbb {Z}\). If \(f\in W_0(\mathbb {R})\), then the piecewise linear continuous function \(\ell _f\) defined by \(\ell _f(k)=f(k)\), \(k\in \mathbb {Z}\), belongs to \(W_0(\mathbb {R})\) as well. Moreover, \(\Vert \ell _f\Vert _{W_0}\le \Vert f\Vert _{W_0}\). Similar relations are established for more advanced Wiener algebras. These results are supplemented by numerous applications. In particular, new necessary and sufficient conditions are proved for a trigonometric series to be a Fourier series and new properties of \(W_0\) are established.



中文翻译:

协调形式的维纳代数和三角级数

\(W_0(\ mathbb {R})\)为可由Lebesgue可积函数的Fourier积分表示的函数的Wiener Banach代数。在本文中证明,尤其是,当且仅当一个三角函数\(\ sum \ nolimits _ {k =-\ infty} ^ \ infty c_k e ^ {ikt} \)的傅里叶级数如果存在\(W_0(\ mathbb {R})中的\ phi \),使得\(\ phi(k)= c_k \)\(\ mathbb {Z}中的k \)。如果\(f在W_0(\ mathbb {R})\)中,则分段线性连续函数\(\ ell _f \)\(\ ell _f(k)= f(k)\)定义\( k \ in \ mathbb {Z} \)属于\(W_0(\ mathbb {R})\)也一样 此外,\(\ Vert \ ell _f \ Vert _ {W_0} \ le \ Vert f \ Vert _ {W_0} \)。对于更高级的维纳代数也建立了类似的关系。这些结果得到了众多应用的补充。特别地,证明了三角级数成为傅立叶级数的新的必要条件和充分条件,并建立了\(W_0 \)的新性质。

更新日期:2021-03-10
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