A parallel monte carlo code for simulating collisional N-body systems

Bharath Pattabiraman*, Stefan Umbreit, Wei-Keng Liao, Alok Nidhi Choudhary, Vicky Kalogera, Gokhan Memik, Frederic A Rasio

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

68 Scopus citations


We present a new parallel code for computing the dynamical evolution of collisional N-body systems with up to N 107 particles. Our code is based on the Hénon Monte Carlo method for solving the Fokker-Planck equation, and makes assumptions of spherical symmetry and dynamical equilibrium. The principal algorithmic developments involve optimizing data structures and the introduction of a parallel random number generation scheme as well as a parallel sorting algorithm required to find nearest neighbors for interactions and to compute the gravitational potential. The new algorithms we introduce along with our choice of decomposition scheme minimize communication costs and ensure optimal distribution of data and workload among the processing units. Our implementation uses the Message Passing Interface library for communication, which makes it portable to many different supercomputing architectures. We validate the code by calculating the evolution of clusters with initial Plummer distribution functions up to core collapse with the number of stars, N, spanning three orders of magnitude from 105 to 107. We find that our results are in good agreement with self-similar core-collapse solutions, and the core-collapse times generally agree with expectations from the literature. Also, we observe good total energy conservation, within ≲ 0.04% throughout all simulations. We analyze the performance of the code, and demonstrate near-linear scaling of the runtime with the number of processors up to 64 processors for N = 105, 128 for N = 106 and 256 for N = 107. The runtime reaches saturation with the addition of processors beyond these limits, which is a characteristic of the parallel sorting algorithm. The resulting maximum speedups we achieve are approximately 60×, 100×, and 220×, respectively.

Original languageEnglish (US)
Article number15
JournalAstrophysical Journal, Supplement Series
Issue number2
StatePublished - Feb 2013


  • galaxies: clusters: general
  • globular clusters: general
  • methods: numerical

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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