SC21 Proceedings

The International Conference for High Performance Computing, Networking, Storage, and Analysis

A 400 Trillion-Grid Vlasov Simulation on Fugaku Supercomputer: Large-Scale Distribution of Cosmic Relic Neutrinos in a Six-Dimensional Phase Space

Authors: Kohji Yoshikawa (University of Tsukuba); Satoshi Tanaka (Kyoto University, Japan); and Naoki Yoshida (University of Tokyo)

Abstract: We report a Vlasov simulation of cosmic relic neutrinos combined with N-body simulation of cold dark matter in the context of large-scale structure formation in the universe performed on Fugaku supercomputer. Gravitational dynamics of the neutrinos is followed, for the first time, by directly integrating the Vlasov equation in six-dimensional phase space. Our largest simulation combines the Vlasov simulation on 400 trillion grids and 330 billion-body calculations in a self-consistent manner, and reproduces accurately the nonlinear dynamics of neutrinos in the universe. The novel high-order Vlasov solver is optimized by combining an array of state-of-the-art numerical schemes and fully utilizing the SIMD instructions on the A64FX processors.

Time-to-solution of our simulation is an order of magnitude shorter than the largest N-body simulations. The performance scales excellently up to 147,456 nodes (7 million CPU cores) on Fugaku; weak and strong scaling efficiencies are 82% to 96% and 82% to 93%, respectively.

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