GRAPE: A parallel computer dedicated to astrophysical many-body problems

Abstract

GRAPE (GRAvitational PipelinE) is a parallel computer dedicated to solve classical gravitational many-body problems in astrophysics. Its prototype was first designed in 1988, and the machine GRAPE-4 attained its performance at 1 teraflops equivalent in 1995. Now, a sub-petaflops machine is expected to be complete before the beginning of the 21st century by a group that is led by one of the members of the former GRAPE project. In the gravitational N-body problems, calculation of gravitational forces between pairs of bodies attracting each other is the heaviest part of computation. It requires calculations of the order of N 2 for one time-step, which is compared with the other calculations such as the time marching only of the order of N calculations. Therefore, in the GRAPE system, the former is performed on a dedicated computer and the latter on a general-purpose computer as a host machine. Only the former is parallelized; it is easy because we can compute forces between different pairs of bodies independently of each other when the positions of the bodies are given. Since details of GRAPE are already published elsewhere, we discuss in the present paper how such a concept of GRAPE is related to the nature of the problem. A heterogeneous system, in which problem-specific, ultra-speed machines are connected with general-purpose machines, will be one of the solutions for highly computation intensive problems in natural science. Cooperations between computer scientists and computational scientists are urgently needed for its realization.