  Hamiltonian systems are one of the most important class of dynamical systems
with a geometric structure called symplecticity and the numerical algorithms
which can preserve such geometric structure are of interest. In this article we
study the construction of symplectic (partitioned) Runge-Kutta methods with
continuous stage, which provides a new and simple way to construct symplectic
(partitioned) Runge-Kutta methods in classical sense. This line of construction
of symplectic methods relies heavily on the expansion of orthogonal polynomials
and the simplifying assumptions for (partitioned) Runge-Kutta type methods.
