Self-dual Leonard pairs

Abstract

Let $\F$ denote a field and let $V$ denote a vector space over $\F$ with finite positive dimension. Consider a pair $A,A^{\ast }$ of diagonalizable $\F$-linear maps on $V$, each of which acts on an eigenbasis for the other one in an irreducible tridiagonal fashion. Such a pair is called a Leonard pair. We consider the self-dual case in which there exists an automorphism of the endomorphism algebra of $V$ that swaps $A$ and $A^{\ast }$. Such an automorphism is unique, and called the duality $A\leftrightarrow A^{\ast }$. In the present paper we give a comprehensive description of this duality. In particular, we display an invertible $\F$-linear map $T$ on $V$ such that the map $X\mapsto TX{T}^{-1}$ is the duality $A\leftrightarrow A^{\ast }$. We express $T$ as a polynomial in $A$ and $A^{\ast }$. We describe how $T$ acts on $4$ flags, $12$ decompositions, and 24 bases for $V$.

25 pages

References in corpus (2)

• Two linear transformations each tridiagonal with respect to an eigenbasis of the other; an algebraic approach to the Askey scheme of orthogonal polynomials
• Totally bipartite tridiagonal pairs