I. Gutman et al. have recently conjectured that the energy of a graph does not exceed its Laplacian energy. We disprove this conjecture by giving a few small counterexamples and, in addition, an infinite set of counterexamples. Nevertheless, we do show that the standard deviation of eigenvalues of the adjacency matrix of every graph does not exceed the standard deviation of eigenvalues of its Laplacian matrix.
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Univ Stellenbosch, Div Math, Dept Math Sci, ZA-7602 Matieland, South AfricaUniv Stellenbosch, Div Math, Dept Math Sci, ZA-7602 Matieland, South Africa
Andriantiana, Eric Ould Dadah
Wagner, Stephan
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Univ Stellenbosch, Div Math, Dept Math Sci, ZA-7602 Matieland, South AfricaUniv Stellenbosch, Div Math, Dept Math Sci, ZA-7602 Matieland, South Africa