Deville, M., & Mund, E. (1985). Tschebyscheff Pseudospectral Solution of 2nd-order Elliptic-equations With Finite-element Preconditioning. Journal of Computational Physics, 60(3), 517-533. https://doi.org/10.1016/0021-9991(85)90034-8 (Original work published 1985)