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Manuscript Title: High temperature expansion via Schwinger-Dyson equations: the planar rotator model on a triangular lattice.
Authors: P. Butera, R. Cabassi, M. Comi, G. Marchesini
Program title: KAPPA,KP
Catalogue identifier: AATS_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 44(1987)143
Programming language: Fortran.
Computer: VAX8600.
Operating system: VMS (VERSION 4.2).
RAM: 24K words
Word size: 32
Peripherals: disc.
Keywords: High temperature expansion, Planar rotator model, Lattice spin models, Classical O(2) Heisenberg model, Schwinger-dyson equation, Kosterlitz-thouless phase transition.
Classification: 7.8, 23.

Nature of problem:
We describe a Fortran program implementing a new algorithm to compute high temperature expansions for lattice spin models. The case of the planar rotator model on a triangular lattice is illustrated here in detail.

Solution method:
The method relies on the iterative solution of the Schwinger Dyson equations of the model.

Running time:
The test run for the high temperature expansion up to the order 9 took 18 s for computing the K matrix (program KAPPA) and 6 s for each correlation moment (program KP).