Discrete Mathematics & Theoretical Computer Science, Vol 14, No 2 (2012)

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On 4-valent Frobenius circulant graphs

Sanming Zhou


A 4-valent first-kind Frobenius circulant graph is a connected Cayley graph DLn(1, h) = Cay(ℤn, H) on the additive group of integers modulo n, where each prime factor of n is congruent to 1 modulo 4 and H={[1], [h], -[1], -[h]} with h a solution to the congruence equation x2 + 1 ≡0 (n). In [A. Thomson and S. Zhou, Frobenius circulant graphs of valency four, J. Austral. Math. Soc. 85 (2008), 269 13;282] it was proved that such graphs admit `perfect' routing and gossiping schemes in some sense, making them attractive candidates for modelling interconnection networks. In the present paper we prove that DLn(1, h) has the smallest possible broadcasting time, namely its diameter plus two, and we explicitly give an optimal broadcasting in DLn(1, h). Using number theory we prove that it is possible to recursively construct larger 4-valent first-kind Frobenius circulants from smaller ones, and we give a methodology for such a construction. These and existing results suggest that, among all 4-valent circulant graphs, 4-valent first-kind Frobenius circulants are extremely efficient in terms of routing, gossiping, broadcasting and recursive construction.

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