Novel symplectic integrators for the Klein-Gordon equation with space- and time-dependent mass

[EN] We consider the numerical time-integration of the non-stationary Klein-Gordon equation with position- and time-dependent mass. A novel class of time-averaged symplectic splitting methods involving double commutators is analyzed and 4th- and 6th-order integrators are obtained. In contrast with standard splitting methods (that contain negative coefficients if the order is higher than two), additional commutators are incorporated into the schemes considered here. As a result, we can circumvent this order barrier and construct high order integrators with positive coefficients and a much reduced number of stages, thus improving considerably their efficiency. The performance of the new schemes is tested on several examples. This work has been funded by Ministerio de Economia, Industria y Competitividad (Spain) through project MTM2016-77660-P (AEI/FEDER, UE). Kopylov has also been partly supported by grant GRISOLIA/2015/A/137 from the Generalitat Valenciana. Bader, P.; Blanes Zamora, S.; Casas, F.; Kopylov, N. (2019). Novel symplectic integrators for the Klein-Gordon equation with space- and time-dependent mass. Journal of Computational and Applied Mathematics. 350:130-138. https://doi.org/10.1016/j.cam.2018.10.011