Nearly outer functions as extreme points in punctured Hardy spaces
نویسندگان
چکیده
The Hardy space $H^1$ consists of the integrable functions $f$ on unit circle whose Fourier coefficients $\widehat f(k)$ vanish for $k<0$. We are concerned with that have some additional (finitely many) holes in spectrum, so we fix a finite set $\mathcal K$ positive integers and consider "punctured" $$H^1_{\mathcal K}:=\{f\in H^1:\,\widehat f(k)=0\,\,\,\text{for all }\, k\in\mathcal K\}.$$ then investigate geometry ball $H^1_{\mathcal K}$. In particular, extreme points identified as those unit-norm K}$ which not too far from being outer (in appropriate sense). This extends theorem de Leeuw Rudin deals classical characterizes its functions. also discuss exposed
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ژورنال
عنوان ژورنال: Advances in Mathematics
سال: 2022
ISSN: ['1857-8365', '1857-8438']
DOI: https://doi.org/10.1016/j.aim.2022.108330