Globally rigid graphs are fully reconstructible (2105.04363v2)

Abstract: A $d$-dimensional framework is a pair $(G,p)$, where $G=(V,E)$ is a graph and $p$ is a map from $V$ to $\mathbb{R}^d$. The length of an edge $uv\in E$ in $(G,p)$ is the distance between $p(u)$ and $p(v)$. The framework is said to be globally rigid in $\mathbb{R}^d$ if the graph $G$ and its edge lengths uniquely determine $(G,p)$, up to congruence. A graph $G$ is called globally rigid in $\mathbb{R}^d$ if every $d$-dimensional generic framework $(G,p)$ is globally rigid. In this paper, we consider the problem of reconstructing a graph from the set of edge lengths arising from a generic framework. Roughly speaking, a graph $G$ is strongly reconstructible in $\mathbb{C}^d$ if the set of (unlabeled) edge lengths of any generic framework $(G,p)$ in $d$-space, along with the number of vertices of $G$, uniquely determine both $G$ and the association between the edges of $G$ and the set of edge lengths. It is known that if $G$ is globally rigid in $\mathbb{R}^d$ on at least $d+2$ vertices, then it is strongly reconstructible in $\mathbb{C}^d$. We strengthen this result and show that under the same conditions, $G$ is in fact fully reconstructible in $\mathbb{C}^d$, which means that the set of edge lengths alone is sufficient to uniquely reconstruct $G$, without any constraint on the number of vertices (although still under the assumption that the edge lengths come from a generic realization). As a key step in our proof, we also prove that if $G$ is globally rigid in $\mathbb{R}^d$ on at least $d+2$ vertices, then the $d$-dimensional generic rigidity matroid of $G$ is connected. Finally, we provide new families of fully reconstructible graphs and use them to answer some questions regarding unlabeled reconstructibility posed in papers.