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arXiv · 2311.14884

A connection between the $A_α$-spectrum and the Lovász theta number

Gabriel Coutinho·Thiago Oliveira
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Abstract

We show that the smallest $α$ so that $αD + (1-α)A \succcurlyeq 0$ is at least $1/\vartheta(\overline{G})$, significantly improving upon a result due to Nikiforov and Rojo (2017). In fact, we display an even stronger connection: if the nonzero entries of $A$ are allowed to vary and those of $D$ vary accordingly, then we show that this smallest $α$ is in fact equal to $1/\vartheta(\overline{G})$. We also show other results obtained as an application of this optimization framework, including a connection to the well-known quadratic formulation for $ω(G)$ due to Motzkin and Straus (1964).

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Gabriel Coutinho, Thiago Oliveira. 2025-04-21. A connection between the $A_α$-spectrum and the Lovász theta number. https://arxiv.org/abs/2311.14884

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