The ABACUS cosmological N-body code

We present ABACUS, a fast and accurate cosmological N-body code based on a new method for calculating the gravitational potential from a static multipole mesh. The method analytically separates the near- and far-field forces, reducing the former to direct 1/r2 summation and the latter to a discrete convolution over multipoles. The method achieves 70 million particle updates per second per node of the Summit supercomputer, while maintaining a median fractional force error of 10^−5. We express the simulation time-step as an event-driven ‘pipeline’, incorporating asynchronous events such as completion of co-processor work, input/output, and network communication. ABACUS has been used to produce the largest suite of N-body simulations to date, the ABACUSSUMMIT suite of 60 trillion particles, incorporating on-the-fly halo finding. ABACUS enables the production of mock catalogues of the volume and resolution required by the coming generation of cosmological surveys.