$k$-path graphs: experiments and conjectures about algebraic connectivity and $\hat{I}\pm$-index

Abstract

This work presents conjectures about eigenvalues of matrices associated with $k$-path graphs, the algebraic connectivity, defined as the second smallest eigenvalue of the Laplacian matrix, and the $\hat{I}\pm$-index, as the largest eigenvalue of the $A_{\hat{I}}\pm$-matrix. For this purpose, a process based on [Discrete Applied Mathematics 164 (2014) 297-303] is presented to generate lists of $k$-path graphs containing all non-isomorphic 2-paths, 3-paths, and 4-paths of order $n$, for $6\le n\le 26,8\le n\le 19$, and $10\le n\le 18$, respectively. Using these lists, exhaustive searches for extremal graphs of fixed order for the mentioned eigenvalues were performed. Based on the empirical results, conjectures are suggested about the structure of extremal $k$-path graphs for these eigenvalues.