Not every graph can be reconstructed from its boundary distance matrix

TL;DR

This paper investigates whether the boundary distance matrix uniquely determines a connected graph, confirming this for some families but providing counterexamples for others, thus clarifying the limits of this graph reconstruction method.

Contribution

It proves the boundary distance matrix uniquely determines certain graph families and identifies specific families where this is not the case.

Findings

Unique reconstruction for block and unicyclic graphs

Counterexamples for split graphs of diameter 3 and distance-hereditary graphs

Clarification of conditions under which boundary distance matrix determines a graph

Abstract

A vertex $v$ of a connected graph $G$ is said to be a boundary vertex of $G$ if for some other vertex $u$ of $G$, no neighbor of $v$ is further away from $u$ than $v$. The boundary $\partial(G)$ of $G$ is the set of all of its boundary vertices. The boundary distance matrix $\hat{D}_G$ of a graph $G=([n],E)$ is the square matrix of order $\kappa$, being $\kappa$ the order of $\partial(G)$, such that for every $i,j\in \partial(G)$, $[\hat{D}_G]_{ij}=d_G(i,j)$. In a recent paper [doi.org/10.7151/dmgt.2567], it was shown that if a graph $G$ is either a block graph or a unicyclic graph, then $G$ is uniquely determined by the boundary distance matrix $\hat{D}_{G}$ of $G$, and it was also conjectured that this statement holds for every connected graph $G$, whenever both the order $n$ and the boundary (and thus also the boundary distance matrix) of $G$ are prefixed. After proving that this conjecture is true for several graph families, such as being of diameter 2, having order at most $n=6$ or being Ptolemaic, we show that this statement does not hold when considering, for example, either the family of split graphs of diameter 3 and order at least $n=10$ or the family of distance-hereditary graphs of order at least $n=8$.