On the distribution of eigenvalues of the reciprocal distance Laplacian matrix of graphs

Abstract

The reciprocal distance Laplacian matrix of a connected graph $G$ is defined as $R{D}^L(G)=RT(G)-RD(G)$, where $RT(G)$ is the diagonal matrix of reciprocal distance degrees and $RD(G)$ is the Harary matrix. Since $R{D}^L(G)$ is a real symmetric matrix, we denote its eigenvalues as ${\lambda }_1(R{D}^L(G))\ge {\lambda }_2(R{D}^L(G))\ge \cdots \ge {\lambda }_n(R{D}^L(G))$. The largest eigenvalue ${\lambda }_1(R{D}^L(G))$ of $R{D}^L(G)$ is called the reciprocal distance Laplacian spectral radius. In this article, we prove that the multiplicity of $n$ as a reciprocal distance Laplacian eigenvalue of $R{D}^L(G)$ is exactly one less than the number of components in the complement graph $\bar{G}$ of $G$. We show that the class of the complete bipartite graphs maximize the reciprocal distance Laplacian spectral radius among all the bipartite graphs with $n$ vertices. Also, we show that the star graph $S_n$ is the unique graph having the maximum reciprocal distance Laplacian spectral radius in the class of trees with $n$ vertices. We determine the reciprocal distance Laplacian spectrum of several well known graphs. We prove that the complete graph $K_n$, $K_n-e$, the star $S_n$, the complete balanced bipartite graph $K_{\frac{n}{2},\frac{n}{2}}$ and the complete split graph $CS(n,\alpha )$ are all determined from the $R{D}^L$-spectrum.

13 pages