Eigenvalues of the adjacency matrix of tetrahedral graphs |
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Authors: | Bose R C Laskar Renu |
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Institution: | (1) University North Carolina, Chapel Hill, N.C., USA |
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Abstract: | A tetrahedral graph is defined to be a graphG, whose vertices are identified with the
unordered triplets onn symbols, such that vertices are adjacent if and only if the corresponding triplets have two symbols in common. Ifn
2
(x) denotes the number of verticesy, which are at distance 2 fromx andA(G) denotes the adjacency matrix ofG, thenG has the following properties: P1) the number of vertices is
. P2)G is connected and regular. P3)n
2
(x) = 3/2(n–3)(n–4) for allx inG. P4) the distinct eigenvalues ofA(G) are –3, 2n–9,n–7, 3(n–3). We show that, ifn > 16, then any graphG (with no loops and multiple edges) having the properties P1)–P4) must be a tetrahedral graph. An alternative characterization of tetrahedral graphs has been given by the authors in 1].This research was supported by the National Science Foundation Grant No. GP-5790, and the Army Research Office (Durham) Grant No. DA-ARO-D-31-12-G910. (Institute of Statistics Mimeo Series No. 571, March 1968.) |
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Keywords: | |
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