Development of electromagnetic particle simulation code in an open system

Abstract

In an electromagnetic particle simulation for magnetic reconnection in an open system, which has a free boundary condition, particles go out and come into the system through the boundary and the number of particles depends on time. Besides, particles are locally attracted due to physical condition. Accordingly, it is hard to realize an adequate load balance with domain decomposition. Furthermore, a vector performance does not become efficient without a large memory size due to a recurrence of array access. In this paper, we parallelise the code with High Performance Fortran. For data layout, all field data are duplicated on each parallel process, but particle data are distributed among them. We invent an algorithm for the open boundary of particles, in which an operation for outgoing and incoming particles is performed in each processor, and the only reduction operation for the number of particles is executed in data transfer. This adequate treatment makes the amount and frequency of data transfer small, and the load balance among processes relevant. Furthermore, a compiler-directive listvec in the gather process dramatically decreases the memory size and improves the vector performance. Vector operation ratio becomes about 99.5% and vector length turns 240 and over. It becomes possible to perform the simulation with 800 million particles in 512 × 128 × 64 meshes. We succeed in opening a path for a large-scale simulation. © Springer-Verlag Berlin Heidelberg 2008.