Yuxiao Shi

Rank and Invertibility of Dense Signed Random Regular Matrices

Let $A$ be the (non-symmetric) adjacency matrix of a uniformly random $d$-regular directed graph on $n$ vertices, and let $Ξ$ be independent of $A$ with i.i.d. Rademacher entries. Suppose that $\min(d,n-d)\geλn$ for some fixed $λ\in(0,1/2]$. We show that there exists $c > 0$, depending only on $λ$, such that \[ \mathbf P_{A,Ξ}\{\operatorname{rank}(A\circΞ)\le n-k\}\le e^{-c nk},\qquad 1\le k\le n. \] As an ingredient in the proof of the rank bound, we use the case $κ=0$ of the following quantitative smallest singular value estimate: \[ \mathbf P_{A,Ξ}\{s_n(A\circΞ)\leκ\} \le Cκ\sqrt n+e^{-c' n}, \qquad κ\ge0, \] where $C,c'>0$ depend only on $λ$.