Random even graphs

We study a random even subgraph of a finite graph G with a general edge-weight p is an element of (0, 1). We demonstrate how it may be obtained from a certain random-cluster measure on G, and we propose a sampling algorithm based on coupling from the past. A random even subgraph of a planar lattice undergoes a phase transition at the parameter-value 1/2p(c), where p(c) is the critical point of the q = 2 random-cluster model on the dual lattice. The properties of such a graph are discussed, and are related to Schramm-Lowner evolutions (SLE).