Burning a binary tree and its generalization

TL;DR

This paper introduces an algorithm for burning trees and improves the upper bound on the burning number, supporting the conjecture for certain subclasses of binary trees.

Contribution

It presents a new algorithm to burn trees and establishes a tighter upper bound on the burning number, advancing the understanding of the burning number conjecture.

Findings

Improved upper bound: $b(T) \\leq \\lceil \\sqrt{n + n_2 + 8}\\,\\rceil -1$ for trees with $n \\geq 50$

Algorithm for burning certain subclasses of binary trees

Proof of the burning number conjecture for specific subclasses of binary trees

Abstract

Graph burning is a graph process that models the spread of social contagion. Initially, all the vertices of a graph $G$ are unburnt. At each step, an unburnt vertex is put on fire and the fire from burnt vertices of the previous step spreads to their adjacent unburnt vertices. This process continues till all the vertices are burnt. The burning number $b(G)$ of the graph $G$ is the minimum number of steps required to burn all the vertices in the graph. The burning number conjecture by Bonato et al. states that for a connected graph $G$ of order $n$, its burning number $b(G) \leq \lceil \sqrt{n} \rceil$. It is easy to observe that in order to burn a graph it is enough to burn its spanning tree. Hence it suffices to prove that for any tree $T$ of order $n$, its burning number $b(T) \leq \lceil \sqrt{n} \rceil$ where $T$ is the spanning tree of $G$. It was proved in 2018 that $b(T) \leq \lceil \sqrt{n + n_2 + 1/4} +1/2 \rceil$ for a tree $T$ where $n_2$ is the number of degree $2$ vertices in $T$. In this paper, we provide an algorithm to burn a tree and we improve the existing bound using this algorithm. We prove that $b(T)\leq \lceil \sqrt{n + n_2 + 8}\rceil -1$ which is an improved bound for $n\geq 50$. We also provide an algorithm to burn some subclasses of the binary tree and prove the burning number conjecture for the same.