English

A distance theorem for inhomogenous random rectangular matrices

Probability 2025-07-28 v2 Metric Geometry

Abstract

Let ARn×(nd)A \in \mathbb{R}^{n \times (n - d)} be a random matrix with independent uniformly anti-concentrated entries satisfying EAHS2Kn(nd)\mathbb{E}\lvert A\rvert_{HS}^2 \leq Kn(n-d) and let HH be the subspace spanned by the columns of AA. Let XRnX \in \mathbb{R}^n be a random vector with uniformly anti-concentrated entries. We show that when 1dλn/logn1 \leq d \leq \lambda n/\log n the distance between between XX and HH satisfies the following following small ball estimate: Pr(dis(X,H)td)(Ct)d+ecn, \Pr\left( \text{dis}(X,H) \leq t\sqrt{d} \right) \leq (Ct)^{d} + e^{-cn}, for some constants λ,c,C>0\lambda,c,C > 0. This extends the distance theorems of Rudelson and Vershynin, Livshyts, and Livshyts,Tikhomirov, and Vershynin by dropping any identical distribution assumptions about the entries of XX and AA. Furthermore it can be applied to prove numerous results about random matrices in the inhomogenous setting. These include lower tail estimates on the smallest singular value of rectangular matrices and upper tail estimates on the smallest singular value of square matrices. To obtain a distance theorem for inhomogenous rectangular matrices we introduce a new tool for this new general ensemble of random matrices, Randomized Logarithmic LCD, a natural combination of the Randomized LCD, used in study of smallest singular values of inhomogenous square matrices, and of the Logarithmic LCD, used in the study of no-gaps delocalization of eigenvectors and the smallest singular values of Hermitian random matrices.

Keywords

Cite

@article{arxiv.2408.06309,
  title  = {A distance theorem for inhomogenous random rectangular matrices},
  author = {Manuel Fernandez},
  journal= {arXiv preprint arXiv:2408.06309},
  year   = {2025}
}

Comments

Added new notation, simplified a number of proofs and fixed a number of typos and misprints

R2 v1 2026-06-28T18:10:41.622Z