The energy of a graph is defined as the sum of the absolute values of its graph eigenvalues (i.e., the sum of its graph spectrum
terms).
Other varieties of graph energy are defined analogously using different matrices associated with a graph (and in particular, a weighted
adjacency matrix).
Cvetković, D. M.; Doob, M.; Sachs, H. Spectra of Graphs. New York: Academic Press, 1980.Gutman, I. "The
Energy of a Graph." In 10. Steiermärkisches Mathematisches Symposium
(Stift Rein, Graz, 1978).Ber. Math.-Statist. Sekt. Forsch. Graz103,
1-22, 1978.Gutman, I. "The Energy of a Graph: Old and New Results."
In Algebraic Combinatorics and Applications (Gößweinstein, 1999).
Berlin: Springer, pp. 196-211, 2001.Li, X.; Shi, Y.; and Gutman, I.
Graph
Energy. New York: Springer, 2012.
