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Mathematical logic, algebra and number theory
Distance-regular graph with intersection array $\{143,108,27;1,12,117\}$ does not exist
A. A. Makhneva, M. M. Isakovab, A. A. Tokbaevab a N.N. Krasovskii Institute of Mathematics and Mechanics of the Ural Branch of the Russian Academy of Sciences, str. S.Kovalevskaya, 16, 620990, Yekaterinburg, Russia
b Kabardino-Balkarian State University named after H.M. Berbekov, str. Chernyshevsky, 175, 360004, Nalchik, Russia
Abstract:
There is a formally self-dual distance-regular graph $\Gamma$ with classical parameters $d=3$, $b=\alpha+1=q$, $\beta=q^2+q-1$ and intersection array $\{(q^2+q-1)(q^2+q+1),(q^2+q)q^2,q^3;1,(q^2+q),q^2(q^2+q+1)\}$. For the graph $\Gamma$ we have the strongly regular graphs $\Gamma_2$ and $\Gamma_3$ ($\Gamma_3$ is pseuqo-geometric for $pG_{q-1}(q^2+q-1,(q^2+q+1)(q-1))$).
It is proved that a distance-regular graph with intersection array $\{143,108,27;1,12,117\}$ ($q=3$) does not exist.
Keywords:
distance-regular graph, formally self-dual graph, triple intersection numbers.
Received October 16, 2021, published March 9, 2023
Citation:
A. A. Makhnev, M. M. Isakova, A. A. Tokbaeva, “Distance-regular graph with intersection array $\{143,108,27;1,12,117\}$ does not exist”, Sib. Èlektron. Mat. Izv., 20:1 (2023), 207–210
Linking options:
https://www.mathnet.ru/eng/semr1581 https://www.mathnet.ru/eng/semr/v20/i1/p207
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Abstract page: | 60 | Full-text PDF : | 23 | References: | 16 |
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