Pseudocyclic 3-class association schemes on 28 points
In [Proc. Conf. algebr. Aspects Comb., Semin. Toronto 1975, 123-155 (1975; Zbl 0326.05023)] \textit{R. Mathon} described a pseudocyclic symmetric 3-class association scheme on 28 points. In this paper we will first present a general method (a 'switching' construction) to construct new symmetric 3-class association schemes from old ones. This method is then applied to the scheme above and yields another scheme with the same parameters. A proof is sketched that these two schemes are the only pseudocyclic symmetric 3-class association schemes on 28 points. Also, a useful reformulation is given of a known existence condition for general pseudocyclic 3-class association schemes.
pseudocyclic symmetric 3-class association scheme on 28 points
scientific article; zbMATH DE number 3891389