Reconstructing a generalized quadrangle with a hemisystem from a 4-class association scheme

Abstract

In 2013, Van Dam, Martin and Muzychuk constructed a cometric Q− antipodal 4-class association scheme from a GQ of order (t2,t), t odd, which has a hemisystem. In this paper we characterize this scheme by its Krein array. The techniques which are used involve the triple intersection numbers introduced by Coolsaet and Jurišić.