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arXiv · 1502.02739

Explicit construction of Ramanujan bigraphs

Cristina Ballantine·Brooke Feigon·Radhika Ganapathy·Janne Kool·Kathrin Maurischat·Amy Wooding
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Abstract

We construct explicitly an infinite family of Ramanujan graphs which are bipartite and biregular. Our construction starts with the Bruhat-Tits building of an inner form of $SU_3(\mathbb Q_p)$. To make the graphs finite, we take successive quotients by infinitely many discrete co-compact subgroups of decreasing size.

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Cristina Ballantine, Brooke Feigon, Radhika Ganapathy, Janne Kool, Kathrin Maurischat, Amy Wooding. 2015-02-09. Explicit construction of Ramanujan bigraphs. https://arxiv.org/abs/1502.02739

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