Romanyuk, A.S., V.S. Romanyuk, K.V. Pozharska, and S.B. Hembars’ka. “Characteristics of Linear and Nonlinear Approximation of Isotropic Classes of Periodic Multivariate Functions”. Carpathian Mathematical Publications 15, no. 1 (June 14, 2023): 78–94. Accessed May 9, 2024. https://journals.pnu.edu.ua/index.php/cmp/article/view/6543.