Conjecture on eigenvector coordinate averages for large S-regular matrices

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Let TT be a large SS-regular matrix, and let T∗T^\ast be the corresponding SS-regular matrix on T⁡S\operatorname{\mathcal{T}}_S. Let U⊂ViU\subset V_i be a sufficiently large subset of the ii-th partition cell of the underlying graph of TT. Let ϕ\phi be a normalized eigenvector of TT with eigenvalue λ\lambda, and let μi\mu_i be defined as in the paper's vertex-distribution proposition. Write ci=∣Vi∣/∣V∣c_i=|V_i|/|V|.

Eigenvector coordinate conjecture. With high probability,

∑v∈Uϕ(u)≈0,\sum_{v\in U}\phi(u)\approx 0,

and

∣V∣∣U∣∑v∈U(ϕ(u))2≈μi(λ)∑jkcjμj(λ).\frac{|V|}{|U|}\sum_{v\in U}\left(\phi(u)\right)^2\approx\frac{\mu_i(\lambda)}{\sum_j^k c_j\mu_j(\lambda)}.

Here the conjecture predicts that most eigenvectors have approximately zero mean on a large subset of a partition cell, while their average squared coordinates are governed by the limiting spectral measures. The preceding results provide the limiting cumulative distributions, but the asserted coordinate-level approximations remain conjectural.

References

Primary source

Matthew B. Crawford, David J. Marchette, William Maxwell and Samuel S. Mendelson, “Spectral properties of random graphs with fixed equitable partition”, arXiv:2311.07675 (2023).

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