The Order Mass Identity of Rooted Forests, with a Direct Proof of the Extended Aldous--Broder Theorem
Year: 2026
Type: preprint
Abstract: The Aldous-Broder algorithm constructs a spanning tree from the first-entrance edges of a covering random walk. Its distribution is known, but deriving it by summing over the orders in which a fixed tree can be discovered remains difficult. In this paper, we evaluate this sum by establishing an order-mass identity for rooted forests. For real matrices with zero row sums, the identity expresses the sum of order weights associated with each root as a principal cofactor of a matrix on the roots, under a nonsingularity condition involving only the sets encountered along the growth orders of the given forest. We prove the identity using linear algebraic tools. With one root, the sum equals one, giving a direct proof of the extended Aldous-Broder theorem for every finite irreducible Markov chain started at a fixed state. With multiple roots, we derive the forest law produced by the stopped covering walk and show how it differs from the weight-proportional forest law. The identity and the resulting tree and forest laws are formalized in Lean 4.
Source: arXiv (Cornell University)
Author: Hugh Zheng
Language: English
Subfield: Mathematical Physics
Field: Mathematics
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7221457967