FASTPM: a new scheme for fast simulations of dark matter and haloes
Abstract
We introduce FASTPM, a highly scalable approximated particle mesh (PM) Nbody solver, which implements the PM scheme enforcing correct linear displacement (1LPT) evolution via modified kick and drift factors. Employing a twodimensional domain decomposing scheme, FASTPM scales extremely well with a very large number of CPUs. In contrast to ComovingLagrangian (COLA) approach, we do not require to split the force or track separately the 2LPT solution, reducing the code complexity and memory requirements. We compare FASTPM with different number of steps (N_{s}) and force resolution factor (B) against three benchmarks: halo mass function from friendsoffriends halo finder; halo and dark matter power spectrum; and crosscorrelation coefficient (or stochasticity), relative to a highresolution TREEPM simulation. We show that the modified time stepping scheme reduces the halo stochasticity when compared to COLA with the same number of steps and force resolution. While increasing N_{s} and B improves the transfer function and crosscorrelation coefficient, for many applications FASTPM achieves sufficient accuracy at low N_{s} and B. For example, N_{s} = 10 and B = 2 simulation provides a substantial saving (a factor of 10) of computing time relative to N_{s} = 40, B = 3 simulation, yet the halo benchmarks are very similar at z = 0. We find that for abundance matched haloes the stochasticity remains low even for N_{s} = 5. FASTPM compares well against less expensive schemes, being only 7 (4) times more expensive than 2LPT initial condition generator for N_{s} = 10 (N_{s} = 5). Some of the applications where FASTPM can be useful are generating a large number of mocks, producing nonlinear statistics where one varies a large number of nuisance or cosmological parameters, or serving as part of an initial conditions solver.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 December 2016
 DOI:
 10.1093/mnras/stw2123
 arXiv:
 arXiv:1603.00476
 Bibcode:
 2016MNRAS.463.2273F
 Keywords:

 methods: numerical;
 galaxies: haloes;
 cosmology: theory;
 dark matter;
 largescale structure of Universe;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 14 pages, 13 figures. The development is hosted at https://github.com/rainwoodman/fastpm . Major revision addressing referee report from MNRAS