SYMMETRIES OF THE PERIODIC TODA LATTICE,WITH AN APPLICATION TO NORMAL FORMS AND PERTURBATIONS OF THE LATTICE WITH DIRICHLET BOUNDARY CONDITIONS

Symmetries of the periodic Toda lattice are expresssed in action-angle coordinates and characterized in terms of the periodic and Dirichlet spectrum of the associated Jacobi matrices. Using these symmetries, the phase space of the lattice with Dirichlet boundary conditions is embedded into the phase space of a higher-dimensional periodic lattice. As an application, we obtain a Birkhoff normal form and a KAM theorem for the lattice with Dirichlet boundary conditions.