Czechoslovak Mathematical Journal, Vol. 71, No. 2, pp. 417-433, 2021
Unbalanced unicyclic and bicyclic graphs with extremal spectral radius
Francesco Belardo, Maurizio Brunetti, Adriana Ciampella
Received September 13, 2019. Published online September 23, 2020.
Abstract: A signed graph $\Gamma$ is a graph whose edges are labeled by signs. If $\Gamma$ has $n$ vertices, its spectral radius is the number $\rho(\Gamma) := \max\{ | \lambda_i(\Gamma) | \colon1 \leq i \leq n \}$, where $\lambda_1(\Gamma) \geq\cdots\geq\lambda_n(\Gamma)$ are the eigenvalues of the signed adjacency matrix $A(\Gamma)$. Here we determine the signed graphs achieving the minimal or the maximal spectral radius in the classes $\frak U_n$ and $\frak B_n$ of unbalanced unicyclic graphs and unbalanced bicyclic graphs, respectively.
Keywords: signed graph; spectral radius; bicyclic graph
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Affiliations: Francesco Belardo, Maurizio Brunetti (corresponding author), Adriana Ciampella, Dipartimento di Matematica e Applicazioni "R. Caccioppoli", Università di Napoli Federico II, I-80126 Napoli, Italy, e-mail: fbelardo@unina.it; mbrunett@unina.it; ciampell@unina.it
