Discussiones Mathematicae Graph Theory 28(2) (2008) 345-359
doi: 10.7151/dmgt.1410

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Hong-Hai Li

College of Mathematic and Information Science
Jiangxi Normal University Nanchang
JiangXi, 330022 People's Republic of China
e-mail: lhh@mail.ustc.edu.cn

Jiong-Sheng Li

Department of Mathematics
University of Science and Technology of China
Anhui, Hefei 230026 People's Republic of China
e-mail: lijs@ustc.edu.cn


In this paper, we established a connection between the Laplacian eigenvalues of a signed graph and those of a mixed graph, gave a new upper bound for the largest Laplacian eigenvalue of a signed graph and characterized the extremal graph whose largest Laplacian eigenvalue achieved the upper bound. In addition, an example showed that the upper bound is the best in known upper bounds for some cases.

Keywords: Laplacian matrix, signed graph, mixed graph, largest Laplacian eigenvalue, upper bound.

2000 Mathematics Subject Classification: 05C50, 15A18.


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Received 15 January 2008
Revised 21 April 2008
Accepted 21 April 2008