Metrically regular bigraphs the square of which are metrically regular graphs are investigated in the case of graphs with 6 distinct eigenvalues (these eigenvalues can have variuos multiplicities).
@article{107432, author = {Vladim\'\i r Vetch\'y}, title = {Metrically regular square of metrically regular bigraphs. II.}, journal = {Archivum Mathematicum}, volume = {028}, year = {1992}, pages = {17-24}, zbl = {0778.05058}, mrnumber = {1201862}, language = {en}, url = {http://dml.mathdoc.fr/item/107432} }
Vetchý, Vladimír. Metrically regular square of metrically regular bigraphs. II.. Archivum Mathematicum, Tome 028 (1992) pp. 17-24. http://gdmltest.u-ga.fr/item/107432/
Association Schemes I, Arch. Math. (Brno) 17 (1981), 173-184. (1981) | MR 0672657 | Zbl 0479.05020
Metrically regular square of metrically regular bigraphs I, Arch. Math. (Brno), Tomus 27b (1992), 183-197. (1992) | MR 1189214