On Laplacian and Signless Laplacian Permanental Polynomials of Some Well-known Graphs

Abstract

The permanent of an $n \times n$ matrix $M = (m_{ij})$ is defined as $\mathrm{per}(M) = \sum_{σ\in S_n} \prod_{i=1}^n m_{i,σ(i)}$, where $S_n$ denotes the symmetric group on $\{1,2,\ldots,n\}$. The permanental polynomial of $M$, is defined by $ψ(M;x) = \mathrm{per}(xI_n - M)$. We study two fundamental variants: the Laplacian permanental polynomial $ψ(L(G);x)$ and signless Laplacian permanental polynomial $ψ(Q(G);x)$ of a graph $G$. A graph is said to be {determined} by its (signless) Laplacian permanental polynomial if no other non-isomorphic graph shares the same polynomial. A graph is combinedly determined when isomorphism is guaranteed by the equality of both polynomials. Characterizing which graphs are determined by their(signless) Laplacian permanental polynomials is an interesting problem. This paper investigates the permanental characterization problem for several families of starlike graphs, including: spider graphs (tree), coconut tree, perfect binary tree, corona product of $C_m$ and $K_n$, and $\bar K_n$ for various values of $m$ and $n$. We establish which of these graphs are determined by their Laplacian or signless Laplacian permanental polynomials, and which require both polynomials for complete characterization. We emphasize that in this manuscript, we have considered a few techniques to compute the permanental polynomial of matrices and their propagation.