Isomorphism classes of association schemes induced by Hadamard matrices

Mitsugu Hirasaka, Kijung Kim, Hyonju Yu

Every Hadamard matrix $H$ of order $n>1$ induces a graph with $4n$ vertices, called the Hadamard graph $\Gamma (H)$ of $H$. Since $\Gamma (H)$ is a distance-regular graph with diameter $4$,…