This is a version of the NBODY6 program by Sverre Aarseth, modified to use the P3T algorithm described in Iwasawa et al. (2015)
The code forks from the NBODY6 source and is modified to use the CMake build system.
If you use this code, please cite the following papers:
- Arnold, Baumgardt & Wang, Accelerating NBODY6 with a graphics processing unit-enabled Particle-Particle Particle-Tree scheme, 2022, MNRAS, 509, 2075.
- Arnold & Baumgardt, Direct N-body simulations of NGC 6397 and its tidal tails, 2025, MNRAS.
The original structure of the code has been retained. Where modifications were required to a Fortran subroutine, a *.tree.f file was created to hold the modified version. Additionally, the code for the GPU-enabled tree code Bonsai is included in the GPU2/lib directory.
To build everything, create a new build directory and run cmake from this directory with the GPU2 directory as the target and then build the targets. For example:
$ git clone [email protected]:anthony-arnold/nbody6-p3t
$ mkdir build
$ cd build
$ cmake ../nbody6-p3t/GPU2
$ make -j4
CMake will generate two targets, nbody7.gpu and nbody7.tree. The former target refers to the original NBODY6 program and the latter is the new program.
The new program takes the same input as the original NBODY6 with a small change. After the initial input which is common to both programs, the following variables are read: NNBOPT and RBUFF. The first variable is unused and can be left as 0. The second variable is the R_buff value required by the P3T algorithm.
Additionally, the opening angle value for the BH-tree algorithm is needed and is set in the environment variable THETA.