96 citations · 283 across the 48 of their papers we have counts for
4 papers · 1 filter
Connectivity concerning the last two subconstituents of a Q-polynomial distance-regular graph
Sebastian M. Cioabă, Jack H. Koolen, Paul Terwilliger
Let be a -polynomial distance-regular graph of diameter . Fix a vertex of and consider the subgraph induced on the union of the last two subconstituents of…
A spectral characterization of the -clique extension of the triangular graphs
Ying-Ying Tan, Jack H. Koolen, Zheng-Jiang Xia
A regular graph is co-edge regular if there exists a constant such that any two distinct and non-adjacent vertices have exactly common neighbors. In this paper, we show tha…
Open problems in the spectral theory of signed graphs
Francesco Belardo, Sebastian M. Cioabă, Jack H. Koolen +1
Signed graphs are graphs whose edges get a sign or (the signature). Signed graphs can be studied by means of graph matrices extended to signed graphs in a natural way. Re…
Non-bipartite distance-regular graphs with a small smallest eigenvalue
Zhi Qiao, Yifan Jing, Jack Koolen
In 2017, Qiao and Koolen showed that for any fixed integer , there are only finitely many such graphs with , where is any fixed number. In this p…