Estimation of the best approximation of periodic functions of two variables by an “angle” in the metric of $L_p$

• Дата: 2004
• Автори: Konopovich, T. O., Конопович, Т. О.
• Формат: Стаття
• Мова: Українська; Англійська
• Опубліковано: Institute of Mathematics, NAS of Ukraine 2004
• Онлайн доступ: https://umj.imath.kiev.ua/index.php/umj/article/view/3834
• Назва журналу: Ukrains’kyi Matematychnyi Zhurnal

We obtain upper bounds in terms of Fourier coefficients for the best approximation by an “angle” and for norms in the metric of $L_p$ for functions of two variables defined by trigonometric series with coefficients such that $a_{l_1 l_2} → 0$ as $l_1 + l_2 → ∞$ and $$\mathop \sum \limits_{k_1 = 0}^...