A comparison of semi-Lagrangian discontinuous Galerkin and spline based Vlasov solvers in four dimensions

TL;DR

This paper compares semi-Lagrangian discontinuous Galerkin and spline-based Vlasov solvers in four dimensions, showing the former's advantages in runtime and scalability for specific plasma physics simulations.

Contribution

It provides a detailed performance comparison between two semi-Lagrangian methods, highlighting the benefits of the discontinuous Galerkin scheme in certain regimes and for parallel scaling.

Findings

Discontinuous Galerkin scheme improves run time for two-stream instability.

Spline interpolation performs better in asymptotic regimes.

DG method scales better due to lack of All-to-All communication.

Abstract

The purpose of the present paper is to compare two semi-Lagrangian methods in the context of the four-dimensional Vlasov--Poisson equation. More specifically, our goal is to compare the performance of the more recently developed semi-Lagrangian discontinuous Galerkin scheme with the de facto standard in Eulerian Vlasov simulation (i.e. using cubic spline interpolation). To that end, we perform simulations for nonlinear Landau damping and a two-stream instability and provide benchmarks for the SeLaLib and sldg codes (both on a workstation and using MPI on a cluster). We find that the semi-Lagrangian discontinuous Galerkin scheme shows a moderate improvement in run time for nonlinear Landau damping and a substantial improvement for the two-stream instability. It should be emphasized that these results are markedly different from results obtained in the asymptotic regime (which favor spline interpolation). Thus, we conclude that the traditional approach of evaluating numerical methods is misleading, even for short time simulations. In addition, the absence of any All-to-All communication in the semi-Lagrangian discontinuous Galerkin method gives it a decisive advantage for scaling to more than 256 cores.