Birkhoff normal form and splitting methods for semi linear Hamiltonian PDEs. Part II: Abstract splitting

TL;DR

This paper proves a normal form result for splitting methods applied to Hamiltonian PDEs, ensuring long-term regularity preservation of numerical solutions under certain conditions, with applications to Schrödinger and wave equations.

Contribution

It establishes a normal form theorem for abstract splitting methods on Hamiltonian PDEs without spatial discretization, under non-resonance conditions, ensuring long-term regularity.

Findings

Normal form result for discrete flow under non-resonance conditions

Long-term regularity preservation of numerical solutions

Applicability to nonlinear Schrödinger and wave equations

Abstract

We consider Hamiltonian PDEs that can be split into a linear unbounded operator and a regular non linear part. We consider abstract splitting methods associated with this decomposition where no discretization in space is made. We prove a normal form result for the corresponding discrete flow under generic non resonance conditions on the frequencies of the linear operator and on the step size. This result implies the conservation of the regularity of the numerical solution associated with the splitting method over arbitrary long time, provided the initial data is small enough. This result holds for numerical schemes controlling the round-off error at each step to avoid possible high frequency energy drift. We apply this results to nonlinear Schr\"odinger equations as well as the nonlinear wave equation.}