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

Trudy Inst. Mat. i Mekh. UrO RAN, 2017 Volume 23, Number 4, Pages 232–242 (Mi timm1482)

Automorphisms of strongly regular graphs with parameters $(1305,440,115,165)$

A. A. Makhnevab, D. V. Paduchikha, M. M. Khamgokovaa

a Krasovskii Institute of Mathematics and Mechanics, Ural Branch of the Russian Academy of Sciences, Yekaterinburg, 620990 Russia
b Ural Federal University, Ekaterinburg, 620002 Russia

Abstract: A graph $\varGamma$ is called $t$-isoregular if, for any $i\le t$ and any $i$-vertex subset $S$, the number $\varGamma(S)$ depends only on the isomorphism class of the subgraph induced by $S$. A graph $\varGamma$ on $v$ vertices is called absolutely isoregular if it is $(v-1)$-isoregular. It is known that each $5$-isoregular graph is absolutely isoregular, and such graphs have been fully described. Each exactly $4$-isoregular graph is either a pseudogeometric graph for pG$_r(2r,2r^3+3r^2-1)$ or its complement. By Izo$(r)$ we denote a pseudogeometric graph for pG$_r(2r,2r^3+3r^2-1)$. Graphs Izo$(r)$ do not exist for an infinite set of values of $r$ ($r=3,4,6,10,\ldots$). The existence of Izo$(5)$ is unknown. In this work we find possible automorphisms for the neighborhood of an edge from Izo$(5)$.

Keywords: isoregular graph, strongly regular graph, pseudogeometric graph.

UDC: 519.17+512.54

MSC: 05C25

Received: 24.04.2017

DOI: 10.21538/0134-4889-2017-23-4-232-242


 English version:
Proceedings of the Steklov Institute of Mathematics (Supplementary issues), 2019, 304, suppl. 1, S112–S122

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