The XY model is an O(2) model of spin statistics.

In d = 2 dimensions, the XY model exhibits an infinite-order topological phase change: the Kosterlitz–Thouless transition.

This program simulates the XY model on a 2-dimensional lattice with periodic boundary conditions, which undergoes the Kosterlitz–Thouless transition at β ≈ 0.5.

Clone and make && make clean.

./xy. Run with --usage or --help for help. It takes arguments for most parameters and will run with sane defaults if none are given.