GRAPE-lA: Special-Purpose Computer for N-body Simulation with a Tree Code
Toshiyuki Fukushige, Tomoyoshi Ito, Junichiro Makino, Toshikazu Ebisuzaki, Daiichiro Sugimoto, Masayuki Umemura · Publications of the Astronomical Society of Japan · 1991
Abstract We have designed and built GRAPE (GRAvity PipE)-lA, a special-purpose computer for N-body simulations using the O(N log N) tree code. GRAPE-lA calculates the gravitational force between particles. A host computer, which is connected to GRAPE-lA, performs all other calculations. GRAPE-lA is different from its predecessor, GRAPE-1, which was designed for the N2 direct summation, regarding three points: a) it can handle particles with different masses, b) the speed of communication between the host computer and GRAPE-lA has been increased, c) and a neighbor list unit has been added. The peak speed of GRAPE-lA is equivalent to 240 Mflops. The effective speed is >200 Mflops for the direct summation, and around 80 Mflops for the tree algorithm. Using GRAPE-lA and the modified tree algorithm code, one time step takes 2 s for N = 4096 and 20 s for N = 32768. GRAPE-lA can complete either a simulation of interacting galaxies (N = 105 , 5000 timesteps) or a cosmological simulation (N = 106 , 500 timesteps) within one week. GRAPE-lA can be also applied to particle-based hydrodynamical simulations such as smoothed-particle hydrodynamics (SPH). The performance of GRAPE-lA is comparable to that of a supercomputer with a peak-speed of 500 Mflops for any type of the direct summation, the modified tree algorithm and SPH.