Maximality of Seidel matrices and switching roots of graphs

Meng Yue Cao, Jack H. Koolen, Akihiro Munemasa, Kiyoto Yoshino

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)


In this paper, we discuss maximality of Seidel matrices with a fixed largest eigenvalue. We present a classification of maximal Seidel matrices of largest eigenvalue 3, which gives a classification of maximal equiangular lines in a Euclidean space with angle arccos 1 / 3. Motivated by the maximality of the exceptional root system E8, we define strong maximality of a Seidel matrix, and show that every Seidel matrix achieving the absolute bound is strongly maximal.

Original languageEnglish
Pages (from-to)1491-1507
Number of pages17
JournalGraphs and Combinatorics
Issue number5
Publication statusPublished - 2021 Sept


  • Adjacency matrices
  • Seidel matrices
  • Switching classes of graphs
  • Two-graphs


Dive into the research topics of 'Maximality of Seidel matrices and switching roots of graphs'. Together they form a unique fingerprint.

Cite this