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Carlo Beenakker
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A "simple" homework question on Minimal perturbation of a Wigner matrix needed to produce an orthogonal top eigenvector

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YCor
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Daniel Li
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A "simple" homework question on Wigner matrix

The instructor proposed a the following statement in the passing and suggested that we think about it (although it is not required):

For any $N \times N$ Wigner matrix, we replace $k$ entries with resampled copy (i.e. the new entries have exact same distribution as the original but are resampled independently). Suppose that $k/N^{5/3}\to\infty$. Denote top eigenvector of original and resampled matrix as $v,v'$. Show that $\mathbb{E}|\langle v,v' \rangle| \to_N0$.

Attempt: the intuition is of course that because of resampling too many entries, the two eigenvectors become less and less correlated. And in high dimensions, two independent vectors distributed uniformly on a ball tend to be orthogonal. But I struggle to explain the $N^{5/3}$ threshold or to formulate a rigorous proof.