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It is known that, for an $m$ dimensional space and an $n\times m$ dimensional random matrix $U$ whose entries are iid Gaussian, then $\|I-(1/n)U^TU\|$ is bounded by $\sqrt{m/n}$ when $n>m$.

If a set $\mathcal{A}\subset \mathbb{R}^m$, when intersecting with unit sphere $\mathcal{S}\subset\mathbb{R}^m$, has Gaussian width $w(\mathcal{A}\cap \mathcal{S}) = w$, then can we say $\max_{x\in\mathcal{A}} \{\|(I-(1/n)U^TU)x\|/\|x\|\}\le w/\sqrt{n}$ with high probability?

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  • $\begingroup$ you probably want A to be a subset of the sphere for the question to make sense $\endgroup$
    – alesia
    Commented Nov 25, 2019 at 20:08
  • $\begingroup$ Yes I talked $w(\mathcal{A}\cap \mathcal{S})$ where $\mathcal{S}$ is unit sphere. $\endgroup$
    – Yue Sun
    Commented Nov 26, 2019 at 17:23

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