Suppose $1< p<\infty$. Let $f$ be a continuous function with compact support defined on $\mathbb{R}$. Does it exist a function $g \in L^p(\mathbb{T})$ such that: $ \widehat{f}|_{\mathbb{Z}}=\widehat{g} $ where $\widehat{f}$ denote the Fourier transform on $\mathbb{R}$ and $\widehat{g}$ the Fourier transform on $\mathbb{T}$ ?
Fourier transform
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functional-analysis
fourier-analysis
1 Answers
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Taking
$ g(x)=\sum_{n=-\infty}^\infty f(x+2\pi n) $ will give the desired result since $g\in C(\mathbb{T})$.
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0@Zouba There is a canonical projection $P:\mathbb{R}\to\mathbb{T}\ $ here and $g(x)=\displaystyle\sum_{y=P^{-1}(x)}f(y)\ $. In the general case I don't know. Perhaps if one is a covering space for another this reasoning still will be correct. – 2011-10-09