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Trudy Instituta Matematiki i Mekhaniki UrO RAN, 2020, Volume 26, Number 3, Pages 14–22
DOI: https://doi.org/10.21538/0134-4889-2020-26-3-14-22
(Mi timm1741)
 

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
References:
Abstract: In the class of distance-regular graphs $\Gamma$ of diameter 3 with a pseudogeometric graph $\Gamma_3$, 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:
$$\big\{c_2(u^2-m^2)+2c_2m-c_2-1,c_2(u^2-m^2),\ (c_2-1)(u^2-m^2)+2c_2m-c_2;1,c_2,u^2-m^2\big\},$$

$$\{mt,(t+1)(m-1),t+1;1,1,(m-1)t\}\ \ \text{for}\ \ m\le t,$$

$$\{lt,(t-1)(l-1),t+1;1,t-1,(l-1)t\},\ \ \text{and}\ \ \{a(p+1),ap,a+1;1,a,ap\}.$$
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 $\Gamma$ with a strongly regular graph $\Gamma_3$.
Funding agency Grant number
Russian Foundation for Basic Research 20-51-53013 ГФЕН_а
This work was supported by the Russian Foundation for Basic Research – the National Natural Science Foundation of China (project no. 20-51-53013_a).
Received: 22.05.2020
Revised: 17.06.2020
Accepted: 13.07.2020
Bibliographic databases:
Document Type: Article
UDC: 519.17
MSC: 05C25
Language: Russian
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
Citation in format AMSBIB
\Bibitem{BelMak20}
\by I.~N.~Belousov, A.~A.~Makhnev
\paper Inverse problems in the class of Q-polynomial graphs
\serial Trudy Inst. Mat. i Mekh. UrO RAN
\yr 2020
\vol 26
\issue 3
\pages 14--22
\mathnet{http://mi.mathnet.ru/timm1741}
\crossref{https://doi.org/10.21538/0134-4889-2020-26-3-14-22}
\elib{https://elibrary.ru/item.asp?id=43893859}
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