Best approximation by trigonometric polynomials of convolution classes generated by some linear combinations of periodic kernels

• Date: 2026
• Main Authors: Serdyuk, A., Sorych, V., Sorych, N., Сердюк, Анатолій, Сорич, Віктор, Сорич, Ніна
• Format: Article
• Language: Ukrainian
• Published: Institute of Mathematics, NAS of Ukraine 2026
• Online Access: https://umj.imath.kiev.ua/index.php/umj/article/view/8934
• Journal Title: Ukrains’kyi Matematychnyi Zhurnal

UDC 517.5 For any nontrivial linear combinations of finitely many Poisson kernels $P_{q_i,\beta}(t)=\displaystyle\sum\nolimits^\infty_{k=0}{q^k_i{\cos \left(kt-\frac{\beta\pi}{2}\right)}},$ $\beta\in {\mathbb R},$ $q_i\in (0,1),$ $i=\overline{1,m},\ m\in\mathbb{N},$ we establish the Nagy condition $...