Finding Adam in noisy trees

Abstract

We consider the problem of finding the root vertex of a random uniform attachment tree, when the union of the unlabeled tree and an Erdős-Rényi random graph $\mathbb{G}(n,p)$ is observed. We prove that, as long as $p=o(\log n/n)$, for any $\epsilon >0$, one can construct a confidence set of vertices of size $K(\epsilon )$ that depends only on $\epsilon$ and not on $n$, such that it contains the root with probability at least $1-\epsilon$. This affirms a conjecture of Crane and Xu (2021). Our approach ranks vertices by their Jordan centrality in the largest component of the subgraph spanned by high-degree vertices. We show that the same approach works in other noise models as well.

56 pages, 6 figures