Conjecture on the largest Fiedler-vector entry in the stochastic block model

Let the stochastic block model have nn vertices, let v2\mathbf{v_2} denote its Fiedler vector, and let g\mathbf{g} be the corresponding indicator vector. The infinity norm is

v2gn.\left\| \mathbf{v_2} - \frac{\mathbf{g}}{\sqrt{n}} \right\|_{\infty}.

Largest-entry conjecture. The largest entry of v2\mathbf{v_2} satisfies

v2gnlognn.\left\| \mathbf{v_2} - \frac{\mathbf{g}}{\sqrt{n}} \right\|_{\infty} \sim \frac{\log n}{n}.

This conjecture concerns the extremal behavior of the Fiedler vector and quantifies the deviation of its most extreme entries from the normalized community-indicator vector. The surrounding discussion motivates it using the higher classification accuracy observed for vertices with extreme-magnitude Fiedler-vector entries; its resolution is not specified in the source.

Sources & referencesView supporting material

Primary source

Adela DePavia and Stefan Steinerberger, “Spectral Clustering Revisited: Information Hidden in the Fiedler Vector”, arXiv:2003.09969 (2020).

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