Past exam of the mathematics course of the University of Cambridge 2026 iii Paper 212 3 a Solution Created 2026-09-24 Updated 2026-09-24
Take an increasing exhaustion of by finite connected vertex sets, identify every vertex outside to one boundary vertex, and choose a uniform spanning tree of the resulting finite wired graph. The weak limit as is the wired uniform spanning forest of .
For Wilson algorithm rooted at infinity, enumerate as . Run a simple random walk from forever and add its chronological loop erasure. Transience makes the infinite loop erasure well-defined. Next, from the first vertex not already in the forest, run an independent random walk until it hits the existing forest; if it never hits, run it forever. Add its loop erasure and continue through the enumeration. Wilson's theorem rooted at infinity says that the resulting forest has the wired uniform spanning forest law.
Wilson algorithm rooted at infinity Created 2026-09-24 Updated 2026-09-24
Wilson's algorithm rooted at infinity builds the wired uniform spanning forest on a transient graph by successively adding loop-erased random walks, run forever when they never hit the forest already constructed.