We describe a new algorithm to compute high-temperature expansions for lattice-spin models. The method, based on a recently proposed iterative solution of the Schwinger-Dyson equations, may be efficiently implemented by a computer program. As an application we calculate the (zero-field) two-point correlation functions and their moments up to 15th order for the planar rotator model on a two-dimensional square lattice. The high-temperature series previously known up to tenth order are thus substantially improved and are analyzed within the framework of the Kosterlitz-Thouless theory.

• Received 12 July 1985

DOI:https://doi.org/10.1103/PhysRevB.33.4725