Discrete nonholonomic LL systems on Lie groups

This paper studies discrete nonholonomic mechanical systems whose configuration space is a Lie group G. Assuming that the discrete Lagrangian and constraints are left-invariant, the discrete Euler-Lagrange equations are reduced to the discrete Euler-Poincare-Suslov equations. The dynamics associated with the discrete Euler-Poincare-Suslov equations is shown to evolve on a subvariety of the Lie group G. The theory is illustrated with the discrete versions of two classical nonholonomic systems, the Suslov top and the Chaplygin sleigh. The preservation of the reduced energy by the discrete flow is observed and discrete momentum conservation is discussed.