## Estrada Index of Graphs

**Authors:** Mohammed Kasim, Fumao Zhang, Qiang Wang

Suppose $G$ is a simple graph. The eigenvalues $\delta_1,
\delta_2,\ldots, \delta_n$ of $G$ are the eigenvalues of its
adjacency matrix $A$. The Estrada index of the graph $G$ is defined
as $EE = EE(G) = \Sigma_{i=1}^{n} e^{\delta_i}$. In this paper the
basic properties of $EE$ are investigated. Moreover, some lower and
upper bounds for the Estrada index in terms of the number of
vertices, edges and the Randic index are obtained. In addition, some
relations between $EE$ and graph energy $E(G)$ are presented.

**Comments:** 6 Pages.

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### Submission history

[v1] 2013-08-05 21:42:13

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