Sesqui-regular graphs with fixed smallest eigenvalue
科研大讨论系列报告
报告题目(Title)：Sesqui-regular graphs with fixed smallest eigenvalue
报告人(Speaker)：Jack Koolen 教授 (中国科学技术大学)
地点(Place)：后主楼1124
时间(Time)：2023 年 9 月 15 日（周五） 10:00--11:00
邀请人(Inviter)：徐敏
报告摘要
A sesqui-regular graph is regular and there exists a constant c such two distinct non-adjacent vertices have either 0 or c
common neighbours. We study these graphs with a valency much larger than the absolute value if its smallest eigenvalue $\theta_{\min}.$ If c is large compared to $|\theta_{min}|$, then the graph is closely related to a strongly regular graphs. On the other hand, it is easy to construct sesqui-regular graphs with unbounded diameter with fixed smallest eigenvalue $-m$ where m is integer and $c$ much smaller than $m$. This talk is based on joint work with Brhane Gebremichel, Jaeyoung Yang, Qian Qian Yang, Masood Ur Rehman, Hongjun Ge.
主讲人简介
Jack Koolen is currently a full professor at the University of Science and Technology of China. He received his Ph.D. from Eindhoven University of Technology in 1994 under supervision of Prof Andries Brouwer. After a few post doc positions in for example Oxford University and Kyushu University, he became an associate professor in POSTECH in Pohang Korea. Since 2013 he is a full professor at the University of Science and Technology of China. His main interest is in algebraic graph theory especially distance-regular graphs. Recently he also got interested in graphs with fixed smallest eigenvalues. He has co-authored a book on phylogenetic combinatorics. He serves as a managing editor of Graphs and Combinatorics also.
