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JOURNALS // Trudy Instituta Matematiki i Mekhaniki UrO RAN // Archive

Trudy Inst. Mat. i Mekh. UrO RAN, 2008 Volume 14, Number 3, Pages 127–131 (Mi timm46)

Amply regular graphs with Hoffman's condition

V. V. Kabanov, S. V. Unegov

Institute of Mathematics and Mechanics, Ural Branch of the Russian Academy of Sciences

Abstract: It is known that, if the minimal eigenvalue of a graph is $-2$, then the graph satisfies Hoffman's condition: for any generated complete bipartite subgraph $K_{1,3}$ (a 3-claw) with parts $\{p\}$ and $\{q_1, q_2,q_3\}$, any vertex distinct from $p$ and adjacent to the vertices $q_1$ and $q_2$ is adjacent to $p$ but not adjacent to $q_3$. We prove the converse statement for amply regular graphs containing a 3-claw and satisfying the condition $\mu>1$.

UDC: 517.17

Received: 09.09.2008


 English version:
Proceedings of the Steklov Institute of Mathematics (Supplementary issues), 2009, 264, suppl. 1, S150–S154

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