Discrete Lagrangian Systems on Graphs. Symplecto-Topological Properties
  Discrete Lagrangian Systems on graphs are considered. Vector-valued closed differential 2-form on the space of solutions is constructed. This form takes values in the first homology group of the graph. This construction generalizes the Symplectic Wronskian for the linear self-adjoint operators on graphs found in 1997 by the first author and used for the needs of the Scattering Theory for graphs with tails 
S.P.Novikov, A.S.Schwarz