Lin–Miao–Guo conjecture on the maximum AαA_{\alpha}-spread

Let GG be a connected simple undirected graph with n5n\geq 5 vertices. Let Aα(G)=αD(G)+(1α)A(G)A_{\alpha}(G)=\alpha D(G)+(1-\alpha)A(G), where D(G)D(G) is the diagonal degree matrix, A(G)A(G) is the adjacency matrix, and α[0,1]\alpha\in[0,1]. If λ1(α)(G)\lambda_1^{(\alpha)}(G) and λn(α)(G)\lambda_n^{(\alpha)}(G) are respectively the largest and smallest eigenvalues of Aα(G)A_{\alpha}(G), define the AαA_{\alpha}-spread by

Sα(G)=λ1(α)(G)λn(α)(G).S_{\alpha}(G)=\lambda_1^{(\alpha)}(G)-\lambda_n^{(\alpha)}(G).

Lin–Miao–Guo conjecture. If 1/2α<11/2\leq\alpha<1, then

Sα(G)Sα(Kin,n1),S_{\alpha}(G)\leq S_{\alpha}(Ki_{n,n-1}),

with equality if and only if GKin,n1G\cong Ki_{n,n-1}.

This conjecture proposes the extremal connected graph for the AαA_{\alpha}-spread when α\alpha is at least one half. The supplied text does not state whether it has been resolved; the notation Kin,n1Ki_{n,n-1} is used in the source but is not defined in the provided context.

Sources & referencesView supporting material

Primary source

Lele Liu, Yi-Zheng Fan, Yi Wang and Wenyan Wang, “On the Spread of Graph-Related Matrices”, arXiv:2412.14789 (2025).

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