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Elsevier, Linear Algebra and its Applications, 1(423), p. 146-154, 2007

DOI: 10.1016/j.laa.2007.01.008

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Star complements and exceptional graphs

Journal article published in 2007 by Dragos Cvetkovic, Peter Rowlinson, Slobodan K. Simic
This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

Let G be a finite graph of order n with an eigenvalue ? of multiplicity k. (Thus the ?-eigenspace of a (0,1)-adjacency matrix of G has dimension k.) A star complement for ? in G is an induced subgraph G-X of G such that |X|=k and G-X does not have ? as an eigenvalue. An exceptional graph is a connected graph, other than a generalized line graph, whose eigenvalues lie in [-2,?). We establish some properties of star complements, and of eigenvectors, of exceptional graphs with least eigenvalue -2.