Yoshimura H., and J. E. Marsden
In this paper we focus on the special case in which the configuration manifold is a Lie group G. In our earlier papers we established the link between the Hamilton-Pontryagin principle and Dirac structures. We begin the paper with the reduction of this principle. The traditional view of Poisson reduction in this case is to reduce T * G with its natural Poisson structure to with its Lie-Poisson structure. However, the basic step of reducing Hamilton's phase space principle already shows that it is important to use for the reduced space, rather than just . In this way, our construction includes both Euler-Poincaré as well as Lie-Poisson reduction. The geometry behind this procedure, which we call Lie-Dirac reduction starts with the standard (i.e., canonical) Dirac structure on T * G (which can be viewed either symplectically or from the Poisson viewpoint) and for each , produces a Dirac structure on . This geometry then simultaneously supports both Euler-Poincaré and Lie-Poisson reduction.
In the last part of the paper, we include nonholonomic constraints, and illustrate this construction with Suslov systems in nonholonomic mechanics, both from the Euler-Poincaré and Lie-Poisson viewpoints.