On the construction of geometric integrators in the RKMK class

We consider the construction of geometric integrators in the class of RKMK methods. Any di erential equation in the form of an in nitesimal generator on a homogeneous space is shown to be locally equivalent to a di erential equation on the Lie algebra corresponding to the Lie group acting on the homogenous space. This way we obtain a distinction between the coordinate-free phrasing of the di erential equation and the local coordinates used. In this paper we study methods based on arbitrary local coordinates on the Lie group manifold. By choosing the coordinates to be canonical coordinates of the rst kind we obtain the original method of Munthe-Kaas [14]. Methods similar to the RKMK method are developed based on the di erent coordinatizations of the Lie group manifold, given by the Cayley transform, diagonal Pad e approximants of the exponential map, canonical coordinates of the second kind, etc. Some numerical experiments are also given.