On $Q$-Polynomial Association Schemes of Small Class

Sho Suda


We show an inequality involving the third largest or second smallest dual eigenvalues of $Q$-polynomial association schemes of class at least three. Also we characterize dual-tight $Q$-polynomial association schemes of class three. Our method is based on tridiagonal matrices and can be applied to distance-regular graphs as well.


Distance-regular graph;Q-polynomial association scheme

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