Department of Physics,Chaohu College,Chaohu 238000,China;
Shanghai Institute of Mathematics and Mechanics,Shanghai University,Shanghai 200072,China;
Shanghai Institute of Mathematics and Mechanics,Shanghai University,Shanghai 200072,China;
Department of Mechanics,Shanghai University,Shanghai 200436,China;
Department of Physics,Chaohu College,Chaohu 238000,China;
Department of Physics,Chaohu College,Chaohu 238000,China;
discrete mechanics; Birkhoff system; discrete Pfaffian; Noether's theorem; first integral;