An energy conservative hp-scheme for light propagation using Liouville’s equation for geometrical opticsRobert A.M. van Gestel, Martijn J.H. Anthonissen, Jan H.M. ten Thije Boonkkamp and Wilbert L. IJzermanEPJ Web Conf., 238 (2020) 02005DOI: https://doi.org/10.1051/epjconf/202023802005