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On distance-regular graphs with intersection arrays {q2−1,q(q−2),q+2;1,q,(q+1)(q−2)}
A. A. Makhnevab, D. V. Paduchikha a Institute of Mathematics and Mechanics, Ural Branch of the Russian Academy of Sciences, Ekaterinburg
b Ural Federal University named after the First President of Russia B. N. Yeltsin, Ekaterinburg
Abstract:
If a distance-regular graph Γ of diameter 3 contains a maximal locally regular 1-code that is last subconstituent perfect, then Γ 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=a3, c=c2, and p=p333 (Jurišić, Vidali). In the first case, Γ has eigenvalue θ2=−1 and the graph Γ3 is pseudogeometric for GQ(p+1,a). If a=c+1, then the graph ˉΓ2 is pseudogeometric for pG2(p+1,2a). If in this case the pseudogeometric graph for the generalized quadrangle GQ(p+1,a) has quasi-classical parameters, then Γ has intersection array {q2−1,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 {q2−1,q(q−2),q+2;1,q,(q+1)(q−2)}.
Keywords:
distance-regular graph, generalized quadrangle, graph automorphism.
Received: 10.09.2020 Revised: 20.12.2020 Accepted: 11.01.2021
Citation:
A. A. Makhnev, D. V. Paduchikh, “On distance-regular graphs with intersection arrays {q2−1,q(q−2),q+2;1,q,(q+1)(q−2)}”, Trudy Inst. Mat. i Mekh. UrO RAN, 27, no. 1, 2021, 146–156
Linking options:
https://www.mathnet.ru/eng/timm1799 https://www.mathnet.ru/eng/timm/v27/i1/p146
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Abstract page: | 134 | Full-text PDF : | 50 | References: | 30 | First page: | 4 |
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