Message passing on the QCDSP supercomputer

The QCDSP machines were designed for lattice gauge calculations. For planning it is crucial to explore this architecture for other computationally intensive tasks. Here I describe an implementation of a simple message passing scheme. With the objective being simplicity, I introduce a small number of generic functions for manipulating a large data set spread over the machine. I test the scheme on three applications: a fast Fourier transform, arbitrary dimension SU(N) pure lattice gauge theory, and the manipulation of Fermionic Fock states through a distributed hash table. These routines compile both on QCDSP and a Unix workstation.Comment: LATTICE99(Algorithms and Machines) - 3 page

Xtoys: cellular automata on xwindows

Xtoys is a collection of xwindow programs for demonstrating simulations of various statistical models. Included are xising, for the two dimensional Ising model, xpotts, for the $q$-state Potts model, xautomalab, for a fairly general class of totalistic cellular automata, xsand, for the Bak-Tang-Wiesenfield model of self organized criticality, and xfires, a simple forest fire simulation. The programs should compile on any machine supporting xwindows.Comment: 4 pages, one figure, uuencoded compressed postscript Contribution to Lattice '95 Also available at http://penguin.phy.bnl.gov/www/papers/BNL-62123.ps.Z Programs available at http://penguin.phy.bnl.gov/www/xtoys/xtoys.htm

Playing with sandpiles

The Bak-Tang-Wiesenfeld sandpile model provdes a simple and elegant system with which to demonstate self-organized criticality. This model has rather remarkable mathematical properties first elucidated by Dhar. I demonstrate some of these properties graphically with a simple computer simulation.Comment: Contribution to the Niels Bohr Summer Institute on Complexity and Criticality; to appear in a Per Bak Memorial Issue of PHYSICA A; 6 pages 3 figure

Surface modes and parity violation in Schwinger model on the lattice

The phase diagram of the Schwinger model on the lattice with Wilson fermions is investigated in the Hartree-Fock approximation. In case of single flavour (not directly amenable to simulations), the calculation indicates the existence of the parity violating phase at both weak and intermediate-to-strong couplings. Hartree-Fock vacuum sustains a nonzero electric field in this broken phase. The phase structure of the model with two flavours is also discussed.Comment: 4 pages, uuencoded compressed PostScript (using uufiles), contribution to LATTICE 9

Chiral anomalies and rooted staggered fermions

A popular approximation in lattice gauge theory is an extrapolation in the number of fermion species away from the four fold degeneracy natural with the staggered fermion formulation. I show that the extrapolation procedure mutilates the expected continuum holomorphic behavior in the quark masses. The conventional resolution proposes canceling the unphysical singularities with a plethora of extra states appearing at finite lattice spacing. This unproven conjecture requires an explicit loss of unitarity and locality. Even if correct, the approach implies large cutoff effects in the low-energy flavor-neutral sector.Comment: 10 pages, no figures; revision includes various clarifications, a changed title, and an additional reference; version to appear in Physics Letters

So you want to be a lattice theorist?

For this after dinner talk I intersperse images of real lattices with a discussion of the motivations for lattice gauge theory and some current unresolved issues.Comment: 6 pages, 7 figures. After dinner talk at Quark confinement and the hadron spectrum VII, Ponta Delgada, Azores, Portugal, 2-7 September 200

Grassmann integrals by machine

I present a numerical algorithm for direct evaluation of multiple Grassmann integrals. The approach is exact and suffers no Fermion sign problems. Memory requirements grow exponentially with the interaction range and the transverse size of the system. Low dimensional systems of order a thousand Grassmann variables can be evaluated on a workstation.Comment: LATTICE98(algorithms), 3 pages, 3 figures, uses espcrc2, revision darkens figure points, adding one from the RIKEN/BNL Supercompute