On the $d$-rigidity phase transition in random graphs
随机图中的 $d$-刚性相变
Yuval Peled
AI总结 研究稀疏随机图中通用 $d$ 维刚性的相变现象,通过局部灵活性参数确定相变阈值并给出刚性秩的渐近估计。
详情
我们研究了稀疏随机图中通用 $d$ 维刚性的相变。主要结果是:对于每个 $d\ge 2$,Erdős--Rényi 随机图 $G\sim G(n,c/n)$ 在已知的显式 $d$-可定向阈值 $c_d$ 处经历 $d$-刚性相变:如果 $c<c_d$,则 $G$ 在通用 $d$-刚性拟阵中渐近几乎必然(a.a.s.)独立。此外,在该区域中 $G$ 没有线性大小的刚性分量:它不包含超过 $3$ 个顶点的诱导 $d$-刚性子图,并且其 $d$-刚性闭包中的最大团的大小至多为 $o(\sqrt n)$。如果 $c>c_d$,则 $G$ 的 $d$-刚性闭包 a.a.s. 包含一个线性大小的巨大团,该团包含图 $((d+1)+d)$-核中除至多 $o(n)$ 个顶点外的所有顶点。我们还给出了超临界区域中 $G$ 的通用 $d$-刚性秩的尖锐渐近估计。更一般地,我们计算了给定度分布的随机图的通用 $d$-刚性秩,误差因子为 $1+o(1)$。例如,我们证明均匀 $n$ 顶点 $k$-正则图 a.a.s. 的秩为 $\min(k/2,d)n+o(n)$。我们的方法是通过一个称为局部灵活性的参数,从随机图的 Galton--Watson 局部弱极限估计其刚性秩。
We study generic $d$-dimensional rigidity in sparse random graphs. Our main result is that for every $d\ge 2$, the Erdős--Rényi random graph $G\sim G(n,c/n)$ undergoes a $d$-rigidity phase transition at the known, explicit, $d$-orientability threshold $c_d$: If $c<c_d$, then $G$ is asymptotically almost surely (a.a.s.) independent in the generic $d$-rigidity matroid. Moreover, in this regime $G$ has no linear-size rigidity components: it contains no induced $d$-rigid subgraphs with more than $3$ vertices, and the largest clique in its $d$-rigidity closure has size at most $o(\sqrt n)$. If $c>c_d$, then $G$ is a.a.s. not independent in the generic $d$-rigidity matroid, and we give a sharp asymptotic estimate for its rank. In addition, the $d$-rigidity closure of $G$ has a giant clique of linear size, which contains all but at most $o(n)$ vertices of the $((d+1)+d)$-core of the graph. More generally, we compute, up to a $1+o(1)$ factor, the generic $d$-rigidity rank of random graphs with a given degree distribution. For example, we show that the uniform $n$-vertex $k$-regular graph a.a.s. has rank $\min(k/2,d)n+o(n).$ Our approach is to estimate the rigidity rank of a random graph from its Galton--Watson local weak limit, using a parameter that we call {\em local flexibility}.