报告题目 (Title)：Distance-regular graphs whose q-distance matrix has exactly one positive eigenvalue （关于q-距离矩阵恰有一个正特征值的距离正则图）
报告人 (Speaker)：Jack Koolen 教授（中国科学技术大学）
报告时间 (Time)：2023年6月28日(周三) 10:00
报告地点 (Place)：校本部E408
邀请人(Inviter)：杨倩倩
报告摘要：The q distance matrix D_q of a connected graph is defined by (D_q)_{xy} = 1 + 1/q + \cdots+ 1/{q^{d-1}} when d(x, y)= d \geq 1 and 0 otherwise. In this talk we study this matrix for the class of distance-regular and show that if it has only one positive eigenvalue it must have certain nice properties. I also show that this happens for many infinite families of distance-regular graphs. This is based on joint work with Sakander Hayat, Mamonn Abdullah and Brhane Gebremichel.