A distance-regular graph $\Gamma$ with intersection array $\{176,135,32,1;1,16,135,176\}$ is an $AT4$-graph. Its antipodal quotient $\bar\Gamma$ is a strongly regular graph with parameters $(672,176$, $40,48)$. In both graphs the neighborhoods of vertices are strongly regular with parameters $(176,40,12,8)$. We study the automorphisms of these graphs. In particular, the graph $\Gamma$ is not arc-transitive. If $G=\mathrm{Aut}\,(\Gamma)$ contains an element of order 11, acts transitively on the vertex set of $\Gamma$, and $S(G)$ fixes each antipodal class, then the full preimage of the group $(G/S(G))'$ is an extension of a group of order 3 by $M_{22}$ or $U_6(2)$. We describe automorphism groups of strongly regular graphs with parameters $(176,40,12,8)$ and $(672,176,40,48)$ in the vertex-symmetric case.
Keywords: strongly regular graph, distance-regular graph, graph automorphism.
The paper was received by the Editorial Office on Dezember 26, 2017.
Funding Agency:
Russian Science Foundation ((Grant Number: 14-11-00061-П).
A.A.Makhnev. Dr. Phys.-Math. Sci., Prof., Krasovskii Institute of Mathematics and Mechanics, Ural Branch of the Russian Academy of Sciences, Yekaterinburg, 620990 Russia,
e-mail: makhnev@imm.uran.ru
D.V.Paduchikh. Dr. Phys.-Math. Sci., Krasovskii Institute of Mathematics and Mechanics, Ural Branch of the Russian Academy of Sciences, Yekaterinburg, 620990 Russia,
e-mail: dpaduchikh@gmail.com
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