  The Accurate Particle Tracer (APT) code is designed for large-scale particle
simulations on dynamical systems. Based on a large variety of advanced
geometric algorithms, APT possesses long-term numerical accuracy and stability,
which are critical for solving multi-scale and non-linear problems. Under the
well-designed integrated and modularized framework, APT serves as a universal
platform for researchers from different fields, such as plasma physics,
accelerator physics, space science, fusion energy research, computational
mathematics, software engineering, and high-performance computation. The APT
code consists of seven main modules, including the I/O module, the
initialization module, the particle pusher module, the parallelization module,
the field configuration module, the external force-field module, and the
extendible module. The I/O module, supported by Lua and Hdf5 projects, provides
a user-friendly interface for both numerical simulation and data analysis. A
series of new geometric numerical methods and key physical problems, such as
runaway electrons in tokamaks and energetic particles in Van Allen belt, have
been studied using APT. As an important realization, the APT-SW version has
been successfully distributed on the world's fastest computer, the Sunway
TaihuLight supercomputer, by supporting master-slave architecture of Sunway
many-core processors.
