On Laplacian Estrada Index of Union and Cartesian Product of Graphs


Harishchandra S. Ramane, Gouramma A. Gudodagi, Abdollah Alhevaz




The Estrada index $EE$ of a graph $G$ of order $n$ is defined as the sum of the terms $e^{\lambda_i}$, $i = 1, 2, \ldots , n$, where $\lambda_1, \lambda_2, \ldots , \lambda_n$ are its adjacency eigenvalues. The Laplacian Estrada index $LEE$ of a graph $G$ is defined as the sum of the terms $e^{\mu_i}$, $i = 1, 2, \ldots , n$, where $\mu_1, \mu_2, \ldots , \mu_n$ are the Laplacian eigenvalues of $G$. In this paper we have obtained the upper bounds for the Laplacian Estrada index of union of graphs and computed Laplacian Estrada index of Cartesian product of some graphs.