Integral Cayley graphs defined by greatest common divisors
The electronic journal of combinatorics, Tome 18 (2011) no. 1
An undirected graph is called integral, if all of its eigenvalues are integers. Let $\Gamma =Z_{m_1}\otimes \ldots \otimes Z_{m_r}$ be an abelian group represented as the direct product of cyclic groups $Z_{m_i}$ of order $m_i$ such that all greatest common divisors $\gcd(m_i,m_j)\leq 2$ for $i\neq j$. We prove that a Cayley graph $Cay(\Gamma,S)$ over $\Gamma$ is integral, if and only if $S\subseteq \Gamma$ belongs to the the Boolean algebra $B(\Gamma)$ generated by the subgroups of $\Gamma$. It is also shown that every $S\in B(\Gamma)$ can be characterized by greatest common divisors.
@article{10_37236_581,
author = {Walter Klotz and Torsten Sander},
title = {Integral {Cayley} graphs defined by greatest common divisors},
journal = {The electronic journal of combinatorics},
year = {2011},
volume = {18},
number = {1},
doi = {10.37236/581},
zbl = {1217.05105},
url = {http://geodesic.mathdoc.fr/articles/10.37236/581/}
}
Walter Klotz; Torsten Sander. Integral Cayley graphs defined by greatest common divisors. The electronic journal of combinatorics, Tome 18 (2011) no. 1. doi: 10.37236/581
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