Symmetry reduction of discrete Lagrangian mechanics on Lie groups
Open Access Publications from the University of California

## Symmetry reduction of discrete Lagrangian mechanics on Lie groups

• Author(s): Marsden, Jerrold E.
• Pekarsky, Sergey
• Shkoller, Steve
• et al.

## Published Web Location

https://arxiv.org/pdf/math/0004018.pdf
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Abstract

For a discrete mechanical system on a Lie group $G$ determined by a (reduced) Lagrangian $\ell$ we define a Poisson structure via the pull-back of the Lie-Poisson structure on the dual of the Lie algebra ${\mathfrak g}^*$ by the corresponding Legendre transform. The main result shown in this paper is that this structure coincides with the reduction under the symmetry group $G$ of the canonical discrete Lagrange 2-form $\omega_\mathbb{L}$ on $G \times G$. Its symplectic leaves then become dynamically invariant manifolds for the reduced discrete system. Links between our approach and that of groupoids and algebroids as well as the reduced Hamilton-Jacobi equation are made. The rigid body is discussed as an example.

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