scholarly journals A Characterization of Q-Polynomial Distance-Regular Graphs Using the Intersection Numbers

2018 ◽  
Vol 34 (5) ◽  
pp. 863-877
Author(s):  
Supalak Sumalroj
2021 ◽  
Vol 28 (4) ◽  
Author(s):  
Ying Ying Tan ◽  
Xiaoye Liang ◽  
Jack Koolen

In the survey paper by Van Dam, Koolen and Tanaka (2016), they asked to classify the thin $Q$-polynomial distance-regular graphs. In this paper, we show that a thin distance-regular graph with the same intersection numbers as a Grassmann graph $J_q(n, D)~ (n \geqslant 2D)$ is the Grassmann graph if $D$ is large enough.


2007 ◽  
Vol 75 (3) ◽  
pp. 420-423 ◽  
Author(s):  
V. V. Kabanov ◽  
A. A. Makhnev ◽  
D. V. Paduchikh

10.37236/2289 ◽  
2012 ◽  
Vol 19 (3) ◽  
Author(s):  
Edwin R. Van Dam ◽  
Miquel Angel Fiol

Recently, it has been shown that a connected graph $\Gamma$ with $d+1$ distinct eigenvalues and odd-girth $2d+1$ is distance-regular. The proof of this result was based on the spectral excess theorem. In this note we present an alternative and more direct proof which does not rely on the spectral excess theorem, but on a known characterization of distance regular graphs in terms of the predistance polynomial of degree $d$.


10.37236/7347 ◽  
2018 ◽  
Vol 25 (1) ◽  
Author(s):  
Štefko Miklavič

Let $\Gamma$ denote a bipartite distance-regular graph with diameter $D$. In [Caughman (2004)], Caughman showed that if $D \ge 12$, then $\Gamma$ is $Q$-polynomial if and only if one of the following (i)-(iv) holds: (i) $\Gamma$ is the ordinary $2D$-cycle, (ii) $\Gamma$ is the Hamming cube $H(D,2)$, (iii) $\Gamma$ is the antipodal quotient of the Hamming cube $H(2D,2)$, (iv) the intersection numbers of $\Gamma$ satisfy $c_i = (q^i - 1)/(q-1)$, $b_i = (q^D-q^i)/(q-1)$ $(0 \le i \le D)$, where $q$ is an integer at least $2$. In this paper we show that the above result is true also for bipartite distance-regular graphs with $D \in \{9,10,11\}$.


Sign in / Sign up

Export Citation Format

Share Document