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Manuscript Title: A fast vectorized program for the CDC CYBER 205 to simulate the Ising spin glass in three dimensions.
Authors: G. Bhanot, R. Salvador, D. Duke, K.J.M. Moriarty
Program title: GLASS
Catalogue identifier: ABDA_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 49(1988)465
Programming language: Fortran.
Computer: CDC CYBER 205.
Operating system: CDC CYBER 205 SERIES 642, VSOS 2.2.
Word size: 64
Keywords: Statistical physics, Thermodynamics, Ising spin glass, Phase transitions, Multispin coding.
Classification: 23.

Nature of problem:
Equilibrium configurations of the three-dimensional Ising spin glass model are generated for 64 arbitrary (+-1) bond distributions using a highly vectorized code and multispin coding.

Solution method:
Sixty-four independent lattices of spins (with periodic boundary conditions) are stored in one vector using multispin coding. For an arbitrary bond configuration and a given inverse temperature Beta, these lattices are simultaneously updated using the Metropolis algorithm by a technique previously invented for the Ising model. The peak updating speed is 80 million spin updates per second which is achieved on a 20**3 lattice.

For peak performance, the program uses the same set of random numbers (in randomly shuffled order) on all sixty-four lattices. This means that the temperature that the simulation is done at is slightly different from the temperature intended. The program computes the actual simulation temperature and reports it as Beta eff (=1/temperature). There is also a parameter (IBE) that can be set to 0 to suppress the use of the same set of random numbers on all 64 lattices. This will eliminate the temperature shift at the cost of reduced program speed. The lattice size (the parameter L in the program) must be even and less than 51. Larger lattice sizes can be incorporated using time slicing.

Running time:
The test run on a 20**3 lattice with 30,000 sweeps took 279 seconds on a 2-pipe, 4-Megawood CDC CYBER 205 at Florida State University, Tallahassee, Florida.