Lattice QCD with two dynamical Wilson fermions on APE100 parallel systems

The cost for stochastic sampling of quantum chromodynamics (QCD) vacuum con figurations outweighs by far the costs of the remaining computational tasks in Lattice QCD, due to the non-local forces arising from the dynamics of f ermion loops in the vacuum fluctuations. The evaluation of quality and henc e efficiency of sampling algorithms is largely determined by the assessment of their decorrelation capacity along the Monte Carlo time series. In orde r to gain control over statistical errors, state-of-the-art research and de velopment on QCD sampling algorithms need substantial amount of teraflops-h ours. Over the past years two German-Italian collaborations, SESAM and T ch i L, carried out exploratory simulations, joining their resources in a meta -computing effort on various computer platforms in Italy and Germany. In th is article, we shall discuss the practical aspects of this work, present hi ghlights of autocorrelation measurements, illustrate the impact of unquench ing on some fundamental parameters of QCD and describe the lessons to be le arned for future, more realistic computer experiments of this kind. (C) 199 9 Elsevier Science B.V. All rights reserved.