Distance-regular graphs where the distance-d graph has fewer distinct eigenvalues
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Let the Kneser graph K of a distance-regular graph $\Gamma$ be the graph on the same vertex set as $\Gamma$, where two vertices are adjacent when they have maximal distance in $\Gamma$. We study the situation where the Bose-Mesner algebra of $\Gamma$ is not generated by the adjacency matrix of K. In particular, we obtain strong results in the so-called `half antipodal' case.
CitationFiol, M.; Brouwer, A. Distance-regular graphs where the distance-d graph has fewer distinct eigenvalues. "Linear algebra and its applications", 2015, vol. 480, p. 115-126.