The discrete variational principle in Hamiltonian formalism and first integrals
Hamilton形式的离散变分原理和第一积分

The aim of this paper is to show that first integrals of discrete equation of motion for Hamiltonian systems can be determined explicitly by investigating the invariance properties of the discrete Lagrangian in phase space. The result obtained is a discrete analog of the theorem of Noether in the Calculus of variations.