Parallel computing and quantum chromodynamics

The study of Quantum Chromodynamics (QCD) remains one of the most challengi ng topics in elementary particle physics. The lattice formulation of QCD, i n which space-time is treated as a four-dimensional hypercubic grid of poin ts, provides the means for a numerical solution from first principles but m akes extreme demands upon computational performance. High Performance Compu ting (HPC) offers us the tantalising prospect of a verification of QCD thro ugh the precise reproduction of the known masses of the strongly interactin g particles. It is also leading to the development of a phenomenological to ol capable of disentangling strong interaction effects from weak interactio n effects in the decays of one kind of quark into another, crucial for dete rmining parameters of the Standard Model of particle physics. The 1980s saw the first attempts to apply parallel architecture computers t o lattice QCD. The SIMD and MIMD machines used in these pioneering efforts were the ICL DAP and the Cosmic Cube, respectively. These were followed by the Connection Machine, the Meiko i860 Computing Surface and the Intel Hype rcube. The end of the decade witnessed a rise in the development of special purpose dedicated parallel systems, notably the APE machines in Rome, the Columbia machines, the GF-11 system at IBM Research and the QCDPAX project in Tsukuba. The state-of-the-art is represented by the CP-PACS machine at T sukuba, and QCDSP, the latest Columbia machine. We give a brief pedagogic review of lattice QCD, outline the computational methodology used and discuss the sources of systematic error that arise in numerical calculations. We outline some of the early calculations and discu ss parallel architectures and their application to QCD, giving examples of both commercial and special purpose machines. After a short section on rece nt developments, we describe state-of-the-art machines and conclude with th e prospects for the future. (C) 1999 Elsevier Science B.V. All rights reser ved.