arXiv subjects

Caelan Atamanchuk

Publications and source records attributed to Caelan Atamanchuk.

6 recordsLinked to original sources

arXiv2025

The largest common subtree of two random trees

We study the size and structure of the largest common subtree (LCS) between two independent Bienaymé trees conditioned to have size $n$. When the trees are critical with finite $2$nd and $(2+κ)$th moment respectively for some $κ>0$, we prove that the LCS has size of order $\sqrt{n}$, and is approximated by the length of three paths meeting at a central node. Moreover, we show that the largest common subtree between two critical independent Bienaymé trees with size $n$ and finite second moments may be much larger than $\sqrt{n}$, implying that our result is tight. We also pose a number of open questions and suggestions for future research.

math.PR↗

arXiv2025

Kingman's coalescent on a random graph

We introduce a generalization of Kingman's coalescent on $[n]$ that we call the Kingman coalescent on a graph $G = ([n],E)$. Specifically, we generalize a forest valued representation of the coalescent introduced in Addario-Berry and Eslava (2018). The difference between the Kingman coalescent on $G$ and the normal Kingman coalescent on $[n]$ is that two trees $T_1,T_2$ with roots $ρ_1,ρ_2$ can merge if and only if $\{ρ_1,ρ_2\} \in E$. When this process finishes (when there are no trees left that can merge anymore), we are left with a random spanning forest that we call a Kingman forest of $G$. In this article, we study the Kingman coalescent on Erdős-Rényi random graphs, $G_{n,p}$. We derive a relationship between the Kingman coalescent on $G_{n,p}$ and uniform random recursive trees, which provides many answers concerning structural questions about the corresponding Kingman forests. We explore the heights of Kingman forests as well as the sizes of their trees as illustrative examples of how to use the connection. Our main results concern the number of trees, $C_{n,p}$, in a Kingman forest of $G_{n,p}$. For fixed $p \in (0,1)$, we prove that $C_{n,p}$ converges in distribution to an almost surely finite random variable as $n \to \infty$. For $p = p(n)$ such that $p \to 0$ and $np \to \infty$ as $n \to \infty$, we prove that $C_{n,p}$ converges in probability to $\frac{2(1-p)}{p}$.

math.PR↗

arXiv2025

On the size of temporal cliques in subcritical random temporal graphs

A \emph{random temporal graph} is an Erdős-Rényi random graph $G(n,p)$, together with a random ordering of its edges. A path in the graph is called \emph{increasing} if the edges on the path appear in increasing order. A set $S$ of vertices forms a \emph{temporal clique} if for all $u,v \in S$, there is an increasing path from $u$ to $v$. \cite{Becker2023} proved that if $p=c\log n/n$ for $c>1$, then, with high probability, there is a temporal clique of size $n-o(n)$. On the other hand, for $c<1$, with high probability, the largest temporal clique is of size $o(n)$. In this note we improve the latter bound by showing that, for $c<1$, the largest temporal clique is of \emph{constant} size with high probability.

math.PR↗

arXiv2025

Uniform temporal trees

Motivated by the study of random temporal networks, we introduce a class of random trees that we coin \emph{uniform temporal trees}. A uniform temporal tree is obtained by assigning independent uniform $[0,1]$ labels to the edges of a rooted complete infinite $n$-ary tree and keeping only those vertices for which the path from the root to the vertex has decreasing edge labels. The $p$-percolated uniform temporal tree, denoted by $\mathcal{T}_{n,p}$, is obtained similarly, with the additional constraint that the edge labels on each path are all below $p$. We study several properties of these trees, including their size, height, the typical depth of a vertex, and degree distribution. In particular, we establish a limit law for the size of $\mathcal{T}_{n,p}$ which states that $\frac{|\mathcal{T}_{n,p}|}{e^{np}}$ converges in distribution to an $\exponential(1)$ random variable as $n \to \infty$. For the height $H_{n,p}$, we prove that $\frac{H_{n,p}}{np}$ converges to $e$ in probability. Uniform temporal trees show some remarkable similarities to uniform random recursive trees.

math.PR↗

arXiv2024

An Algorithm to Recover Shredded Random Matrices

Given some binary matrix $M$, suppose we are presented with the collection of its rows and columns in independent arbitrary orderings. From this information, are we able to recover the unique original orderings and matrix? We present an algorithm that identifies whether there is a unique ordering associated with a set of rows and columns, and outputs either the unique correct orderings for the rows and columns or the full collection of all valid orderings and valid matrices. We show that there is a constant $c > 0$ such that the algorithm terminates in $O(n^2)$ time with high probability and in expectation for random $n \times n$ binary matrices with i.i.d.\ Bernoulli $(p)$ entries $(m_{ij})_{ij=1}^n$ such that $\frac{c\log^2(n)}{n(\log\log(n))^2} \leq p \leq \frac{1}{2}$.

math.PR↗

arXiv2023

A note on estimating the dimension from a random geometric graph

Let $G_n$ be a random geometric graph with vertex set $[n]$ based on $n$ i.i.d.\ random vectors $X_1,\ldots,X_n$ drawn from an unknown density $f$ on $\R^d$. An edge $(i,j)$ is present when $\|X_i -X_j\| \le r_n$, for a given threshold $r_n$ possibly depending upon $n$, where $\| \cdot \|$ denotes Euclidean distance. We study the problem of estimating the dimension $d$ of the underlying space when we have access to the adjacency matrix of the graph but do not know $r_n$ or the vectors $X_i$. The main result of the paper is that there exists an estimator of $d$ that converges to $d$ in probability as $n \to \infty$ for all densities with $\int f^5 < \infty$ whenever $n^{3/2} r_n^d \to \infty$ and $r_n = o(1)$. The conditions allow very sparse graphs since when $n^{3/2} r_n^d \to 0$, the graph contains isolated edges only, with high probability. We also show that, without any condition on the density, a consistent estimator of $d$ exists when $n r_n^d \to \infty$ and $r_n = o(1)$.

stat.ML↗