Limit-point conjecture for the top eigenvalue vectors of regular graphs

From papers

Let d3d\geq 3 and kk be fixed. For a dd-regular graph GG, write λ1(G)λ2(G)\lambda_1(G)\geq\lambda_2(G)\geq\cdots for its ordered eigenvalues. Define B(d,k)B(d,k) by

B(d,k)={(μ1,μ2,,μk):d=μ1μ2μ3μk2d1}.B(d,k)=\{(\mu_1,\mu_2,\ldots,\mu_k):d=\mu_1\geq\mu_2\geq\mu_3\geq\cdots\geq\mu_k\geq 2\sqrt{d-1}\}.

Top-eigenvalue vector limit-point conjecture. For any d3d\geq 3 and any fixed kk, the set of all limit points of the vectors

(λ1(Gi),λ2(Gi),,λk(Gi))(\lambda_1(G_i),\lambda_2(G_i),\ldots,\lambda_k(G_i))

along infinite sequences GiG_i of dd-regular graphs is exactly B(d,k)B(d,k). This extends the proved one-coordinate result for the second eigenvalue, while the realizability of all admissible vectors remains open.

Progress summary

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Sources & referencesView supporting material

Primary source

Noga Alon and Fan Wei, “The limit points of the top and bottom eigenvalues of regular graphs”, arXiv:2304.01281 (2023).

Additional references

5 papers in this index state this conjecture (2011–2023). The statement above is taken from the most recent of them; the others are arXiv:2204.05287, arXiv:1711.07996, arXiv:1608.08931, arXiv:1108.3805.

Solutions 0

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