Playing with computers

Once (1984-1986) I had the fascinating experience to be involved with the building of a special purpose computer called "PERCOLA". The computer was running until recently in Saclay and has been giving data for over ten years. The first were on the conductivity and superconductivity exponents of percolation published in J. Stat. Phys., Vol.52, p.441-446 (1988) and published in Int.J.Mod.Phys. C, Vol. 1, 207-214 (1990) respectively. The latest results have been published in Int.J.Mod.Phys. C, Vol. 6, 813-818 (1995).

In the past I also did a lot of bit-manipulation for multi-spin coding on vector computers. With John Zabolitzky we established in a paper (J.Comp.Phys. 76, 426-447 (1988)) some world records in size and speed of Ising simulations (on the Cray-2).

In 1992 I was involved in the European Teraflop Initiative and did benchmarking and tests of parallel machines of various type. One of these comparisons on Connexion Machines is given in the following report .

A paper which much impact on computer algorithms is with P.M.C. de Oliveira and T. Penna (Braz. J. of Phys. 26, 677-683 (1997)) about a new canonical Monte Carlo histogram technique which has good precision over a much larger temperature range than usual histogram methods. With my former PhD student Jose Daniel Muñoz who is now professor at the Universidad Nacional de Bogota we extended this method to systems with continuous degrees of freedom as published in a paper in Int.J.Mod.Phys. C, Vol. 10, 95-114 (1999) for the XY model and in a paper published in Comp. Physcs Comm., Vol. 121, p. 13-15 (1999) and in the proceedings of the XII meeting on Computer Simulation Studies in Condensed Matter Physics, p.174-178 (1999) for the more general case.

In Stuttgart I also wrote several reviews about computing in german, for instance for "Wechselwirkungen 2002" and for "Simulation und Visualisierung" and also gave a radio interview .