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Inverse problems in the class of Q-polynomial graphs
I. N. Belousovab, A. A. Makhnevab 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:
In the class of distance-regular graphs Γ of diameter 3 with a pseudogeometric graph Γ3, feasible intersection arrays for the partial geometry were found for networks by Makhnev, Golubyatnikov, and Guo; for dual networks by Belousov and Makhnev; and for generalized quadrangles by Makhnev and Nirova. These authors obtained four infinite series of feasible intersection arrays of distance-regular graphs: {c2(u2−m2)+2c2m−c2−1,c2(u2−m2), (c2−1)(u2−m2)+2c2m−c2;1,c2,u2−m2}, {mt,(t+1)(m−1),t+1;1,1,(m−1)t} for m⩽t, {lt,(t−1)(l−1),t+1;1,t−1,(l−1)t}, and {a(p+1),ap,a+1;1,a,ap}. We find all feasible intersection arrays of Q-polynomial graphs from these series. In particular, we show that, among these infinite families of feasible arrays, only two arrays ({7,6,5;1,2,3} (folded 7-cube) and {191,156,153;1,4,39}) correspond to Q-polynomial graphs.
Keywords:
distance-regular graph, Q-polynomial graph, graph Γ with a strongly regular graph Γ3.
Received: 22.05.2020 Revised: 17.06.2020 Accepted: 13.07.2020
Citation:
I. N. Belousov, A. A. Makhnev, “Inverse problems in the class of Q-polynomial graphs”, Trudy Inst. Mat. i Mekh. UrO RAN, 26, no. 3, 2020, 14–22
Linking options:
https://www.mathnet.ru/eng/timm1741 https://www.mathnet.ru/eng/timm/v26/i3/p14
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Abstract page: | 163 | Full-text PDF : | 46 | References: | 39 | First page: | 6 |
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