Bordenave–Chafaï conjecture for random regular digraph matrices

Let AnA_n be a random regular digraph matrix, meaning a uniformly random element of Mn(d)\mathop{\mathrm{M}}_n(d), where Mn(d)\mathop{\mathrm{M}}_n(d) is the set of n×nn\times n zero-one matrices whose row and column sums are all dd. For a matrix MM, let μM\mu_M denote its empirical spectral distribution. Bordenave–Chafaï conjecture. (1) If d=dnn/2d=d_n\le n/2 and dd\rightarrow\infty as nn\rightarrow\infty, then μ1dAn\mu_{\frac{1}{\sqrt{d}}A_n} converges to the circular law. (2) If d3d\ge 3 is fixed independently of nn, then μAn\mu_{A_n} converges to the oriented Kesten–McKay law on C\mathbb{C}, with density

fKM(w)=1πd2(d1)(d2w2)21wd.f_{KM}(w)=\frac{1}{\pi}\frac{d^2(d-1)}{(d^2-|w|^2)^2}\mathbf{1}_{\\{|w|\le \sqrt{d}\\}}.

These claims predict the limiting spectral distributions of random regular digraph adjacency matrices in both the growing-degree and fixed-degree regimes. The statement is presented as an augmented version of a conjecture of Bordenave and Chafaï; the source does not provide evidence of resolution.

Sources & referencesView supporting material

Primary source

Nicholas A. Cook, “The circular law for random regular digraphs with random edge weights”, arXiv:1508.00208 (2017).

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