An energy conservative hp-scheme for light propagation using Liouville’s equation for geometrical optics Robert A.M. van Gestel, Martijn J.H. Anthonissen, Jan H.M. ten Thije Boonkkamp and Wilbert L. IJzerman EPJ Web Conf., 238 (2020) 02005 Published online: 20 August 2020 DOI: 10.1051/epjconf/202023802005