On Hoffman polynomials of $\lambda$-doubly stochastic irreducible matrices and commutative association schemes

Giusy Monzillo, Safet Penjić

Let $\Gamma$ denote a finite (strongly) connected regular (di)graph with adjacency matrix $A$. The {\em Hoffman polynomial} $h(t)$ of $\Gamma =\Gamma (A)$ is the unique polynomial of smallest degre…