
Journal of Lie Theory 25 (2015), No. 4, 11391165 Copyright Heldermann Verlag 2015 On the Lie Enveloping Algebra of a PostLie Algebra Kurusch EbrahimiFard ICMAT  UAM, Calle Nicolás Cabrera 1315, Campus de Cantoblanco, 28049 Madrid, Spain kurusch@icmat.es Alexander Lundervold Dept. of Computing Mathematics and Physics, Bergen University College, Postboks 7030, 5020 Bergen, Norway alexander.lundervold@hib.no Hans Z. MuntheKaas Dept. of Mathematics, University of Bergen, Postbox 7800, 5020 Bergen, Norway hans.munthekaas@math.uib.no [Abstractpdf] \def\g{{\frak g}} We consider pairs of Lie algebras $\g$ and $\overline{\g}$, defined over a common vector space, where the Lie brackets of $\g$ and $\overline{\g}$ are related via a postLie algebra structure. The latter can be extended to the Lie enveloping algebra ${\cal U}(\g)$. This permits us to define another associative product on ${\cal U}(\g)$, which gives rise to a Hopf algebra isomorphism between ${\cal U}(\overline{\g})$ and a new Hopf algebra assembled from ${\cal U}(\g)$ with the new product.\endgraf For the free postLie algebra these constructions provide a refined understanding of a fundamental Hopf algebra appearing in the theory of numerical integration methods for differential equations on manifolds. In the preLie setting, the algebraic point of view developed here also provides a concise way to develop Butcher's order theory for RungeKutta methods. Keywords: Rooted trees, combinatorial Hopf algebras, postLie algebras, universal enveloping algebras, numerical Lie group integration, geometric numerical integration, Butcher's order theory. MSC: 65L, 53C, 16T [ Fulltextpdf (439 KB)] for subscribers only. 