High order symplectic schemes for the sine-Gordon equation

In this paper, taking the sine-Gordon equation as an example, we present a new method to construct the symplectic schemes for Hamilton PDEs. Different from the previous symplectic methods dealing with PDEs, our method is that to view the PDEs as a Hamilton system in Danach space, then to apply the generating functions method to the Hamilton system. After overcoming successfully the essential difficulties on the calculations of high order variation derivatives, we get the semi-discrete difference schemes for the PDEs with arbitrary order of accuracy in time direction. Furthermore the corresponding modified equations of the infinite dimensional Hamiltonian system are obtained from the semi-discretization. We use the central difference operators to discretize the derivatives in space. Thus the resulting full discrete symplectic schemes can be of any order accuracy. Numerical results on collisions of solitons are also presented to show the effectiveness of the schemes.