“p-Multigrid Method for Fekete-Gauss Spectral Element Approximations of Elliptic Problems”, Commun. Comput. Phys., vol. 5, no. 2-4, pp. 667–682, Apr. 2018, Accessed: Dec. 05, 2025. [Online]. Available: https://global-sci.com/index.php/cicp/article/view/5627