GRAPE Project: An Overview
Toshikazu Ebisuzaki, Junichiro Makino, Toshiyuki Fukushige, Makoto Taiji, Daiichiro Sugimoto, Tomoyoshi Ito, Sachiko K. Okumura · Publications of the Astronomical Society of Japan · 1993
Abstract We are developing a series of special-purpose computers, GRAPE (GRAvity PipE), for the simulation of N-body systems, such as proto-planetary systems, globular clusters, galaxies, and clusters of galaxies. In simulations of N-body systems, almost all computing time is consumed in calculating the gravitational force between particles. GRAPE calculates the forces at high speed using hard-wired pipelines. The host computer, which is connected to GRAPE, sends the positions of particles to GRAPE. Then, GRAPE calculates the force exerted on a particle and sends this value back to the host computer. Using the force calculated by GRAPE, the host computer then integrates the orbits of the particles. We have already developed six different machines (GRAPE-1, GRAPE-lA, GRAPE-2, GRAPE-2A, GRAPE-3, and GRAPE-3A), which are divided into low- and high-accuracy types. Those machines with odd numbers (GRAPE-1, GRAPElA, GRAPE-3, and GRAPE-3A) are among the low-accuracy type. They were designed for simulations of collisionless systems, such as galaxies, in which only the mean potential plays an important role. Simulations of such systems do not require high accuracy in the force calculation. GRAPE-1 and GRAPE-lA are machines made by wire-wrapping. GRAPE-3 is a highly parallel system with 48 full-custom LSI chips (GRAPE chip). Each LSI chip has one GRAPE pipeline. The sustained speed ofGRAPE-3 is 10 Gflops for a 200,000 particle simulation. The machines with even numbers (GRAPE-2 and GRAPE-2A) are among the high-accuracy type. They were designed for collisional systems, such as globular clusters and protoplanetary systems, in which close encounters play an important role. In simulations of such collisional systems, we must calculate the force accurately. "GRAPE-2 was the first machine of the high-accuracy type. GRAPE-2A was designed for applications involving molecular-dynamics simulations, as well as gravitational N-body simulations. GRAPE-2A can calculate the forces of an arbitrary functional form using interpolation tables. The computational speed of GRAPE-2A is 180 Mflops. We are now developing a highly parallel machine, GRAPE-4, in which many GRAPE pipelines (about 1,600) will work in parallel.