Geodesic
On distance-regular graphs with intersection arrays $\{q^2-1,q(q-2),q+2;1,q,(q+1)(q-2)\}$
Trudy Instituta matematiki i mehaniki, Trudy Instituta Matematiki i Mekhaniki UrO RAN, Tome 27 (2021) no. 1, pp. 146-156 Cet article a éte moissonné depuis la source Math-Net.Ru

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If a distance-regular graph $\Gamma$ of diameter 3 contains a maximal locally regular 1-code that is last subconstituent perfect, then $\Gamma$ has intersection array $\{a(p+1),cp,a+1;1,c,ap\}$ or $\{a(p+1),(a+1)p,c;1,c,ap\}$, where $a=a_3$, $c=c_2$, and $p=p^3_{33}$ (Jurišić, Vidali). In the first case, $\Gamma$ has eigenvalue $\theta_2=-1$ and the graph $\Gamma_3$ is pseudogeometric for $GQ(p+1,a)$. If $a=c+1$, then the graph $\bar\Gamma_2$ is pseudogeometric for $pG_2(p+1,2a)$. If in this case the pseudogeometric graph for the generalized quadrangle $GQ(p+1,a)$ has quasi-classical parameters, then $\Gamma$ has intersection array $\{q^2-1,q(q-2),q+2;1,q,(q+1)(q-2)\}$ (Makhnev, Nirova). In this paper, we find possible automorphisms of a graph with intersection array $\{q^2-1,q(q-2),q+2;1,q,(q+1)(q-2)\}$.
Keywords: distance-regular graph, generalized quadrangle
Mots-clés : graph automorphism. 
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     title = {On distance-regular graphs with intersection arrays $\{q^2-1,q(q-2),q+2;1,q,(q+1)(q-2)\}$},
     journal = {Trudy Instituta matematiki i mehaniki},
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A. A. Makhnev; D. V. Paduchikh. On distance-regular graphs with intersection arrays $\{q^2-1,q(q-2),q+2;1,q,(q+1)(q-2)\}$. Trudy Instituta matematiki i mehaniki, Trudy Instituta Matematiki i Mekhaniki UrO RAN, Tome 27 (2021) no. 1, pp. 146-156. http://geodesic.mathdoc.fr/item/TIMM_2021_27_1_a14/

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