The purpose of this chapter is to introduce an extended discrete gradient formula for the multi-frequency oscillatory Hamiltonian system with the Hamiltonianrepresents generalized momenta, and M ∈ R d×d is a symmetric and positive semi-definite matrix. The solution of this system is a nonlinear oscillator. Basically, many nonlinear oscillatory mechanical systems with a partitioned Hamiltonian function lend themselves to this approach. The extended discrete gradient formula exactly preserves the energy H(p, q). Some properties of the new formula are given. The convergence is analysed for the implicit schemes based on the discrete gradient formula, and it turns out that the convergence is independent of M , which is a significant property for numerically solving the oscillatory Hamiltonian system. This implies that a larger stepsize can be chosen for the extended energypreserving scheme than for the traditional discrete gradient methods in applications to multi-frequency oscillatory Hamiltonian systems. Illustrative examples show that the new schemes are greatly superior to the traditional discrete gradient methods in the literature.
MotivationThe design and analysis of numerical integration methods for nonlinear oscillators is an important problem that has received a great deal of attention in the last few years. It is known that the traditional approach to deriving numerical integration methods is based on the natural procedure of discretizing the differential equation in such a way as to make the local truncation errors associated with the discretization as small as possible. A relatively new and increasingly important area in numerical integration methods is geometric integration. A numerical integration method is called geometric if it exactly preserves one or more physical/geometric properties