Combinatorica ( IF 1.0 ) Pub Date : 2025-04-03 , DOI: 10.1007/s00493-025-00149-z
Alan Lew , Eran Nevo , Yuval Peled , Orit E. Raz
Jordán and Tanigawa recently introduced the d-dimensional algebraic connectivity \(a_d(G)\) of a graph G. This is a quantitative measure of the d-dimensional rigidity of G which generalizes the well-studied notion of spectral expansion of graphs. We present a new lower bound for \(a_d(G)\) defined in terms of the spectral expansion of certain subgraphs of G associated with a partition of its vertices into d parts. In particular, we obtain a new sufficient condition for the rigidity of a graph G. As a first application, we prove the existence of an infinite family of k-regular d-rigidity-expander graphs for every \(d\ge 2\) and \(k\ge 2d+1\). Conjecturally, no such family of 2d-regular graphs exists. Second, we show that \(a_d(K_n)\ge \frac{1}{2}\left\lfloor \frac{n}{d}\right\rfloor \), which we conjecture to be essentially tight. In addition, we study the extremal values \(a_d(G)\) attains if G is a minimally d-rigid graph.
中文翻译:

刚度扩展器图形
Jordán 和 Tanigawa 最近引入了图 G 的 d 维代数连通性 \(a_d(G)\)。这是 G 的 d 维刚度的定量测量,它推广了经过充分研究的图谱扩展概念。我们提出了一个新的 \(a_d(G)\) 下限,该下限是根据 G 的某些子图的光谱扩展来定义的,这些子图与将其顶点划分为 d 部分相关联。特别是,我们获得了图 G 刚度的新充分条件。作为第一个应用,我们证明了每个 \(d\ge 2\) 和 \(k\ge 2d+1\) 存在一个无限的 k 规则 d 刚性扩展器图族。从推测上,不存在这样的 2d 正则图族。其次,我们展示了 \(a_d(K_n)\ge \frac{1}{2}\left\lfloor \frac{n}{d}\right\rfloor \),我们推测它本质上是紧密的。此外,我们还研究了如果 G 是一个最小 d 刚性图,则 \(a_d(G)\) 会达到的极值。