Average Nikolskii factors for random trigonometric polynomials

For $1\le p,q\le \infty $, the Nikolskii factor for a trigonometric polynomial $T_{{\mathbf{a}}}$ is defined by $$ N_{p,q}(T_{{\mathbf{a}}})= \frac{\|T_{{\mathbf{a}}}\|_{q}}{\|T_{{\mathbf{a}}}\|_{p}},\ \ T_{{ \mathbf{a}}}(x)=a_{1}+\sum \limits ^{n}_{k=1}(a_{2k}\sqrt{2}\cos kx+a_{2k+1} \sqrt{2}\sin kx). $$ We study this average Nikolskii factor for random trigonometric polynomials with independent $N(0,\sigma ^{2})$ coefficients and obtain the exact orders. For $1\leq p< q<\infty $, the average Nikolskii factor is of order $n^{0}$ (i.e., constant), as compared to the worst case bound of order $n^{1/p-1/q}$, and for $1\leq p< q=\infty $, the average Nikolskii factor is of order $(\ln n)^{1/2}$ as compared to the worst case bound of order $n^{1/p}$. We also give the generalization to random multivariate trigonometric polynomials.

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Publication Details

Journal
Journal of Inequalities and Applications
Published
2026-04-27
DOI
https://doi.org/10.1186/s13660-026-03484-x
Primary Topic
Geometry and complex manifolds
Type
article
Field-Weighted Citation Impact
0.00

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article

Average Nikolskii factors for random trigonometric polynomials

Jiaxin Geng, Heping Wang, Jiansong Li, Yun Ling
Journal of Inequalities and Applications
Geometry and complex manifolds
article

Average Nikolskii factors for random trigonometric polynomials

Jiaxin Geng, Heping Wang, Jiansong Li, Yun Ling
article en

Abstract

For $1\le p,q\le \infty $, the Nikolskii factor for a trigonometric polynomial $T_{{\mathbf{a}}}$ is defined by $$ N_{p,q}(T_{{\mathbf{a}}})= \frac{\|T_{{\mathbf{a}}}\|_{q}}{\|T_{{\mathbf{a}}}\|_{p}},\ \ T_{{ \mathbf{a}}}(x)=a_{1}+\sum \limits ^{n}_{k=1}(a_{2k}\sqrt{2}\cos kx+a_{2k+1} \sqrt{2}\sin kx). $$ We study this average Nikolskii factor for random trigonometric polynomials with independent $N(0,\sigma ^{2})$ coefficients and obtain the exact orders. For $1\leq p< q<\infty $, the average Nikolskii factor is of order $n^{0}$ (i.e., constant), as compared to the worst case bound of order $n^{1/p-1/q}$, and for $1\leq p< q=\infty $, the average Nikolskii factor is of order $(\ln n)^{1/2}$ as compared to the worst case bound of order $n^{1/p}$. We also give the generalization to random multivariate trigonometric polynomials.

Journal of Inequalities and Applications
Capital Normal University (CN)
National Natural Science Foundation of China
Openalex Percentile: Top 94%
Geometry and complex manifolds
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