
arXiv: 1409.4333
Fix an algebraically closed field $\mathbb{F}$ and an integer $d \geq 3$. Let $V$ be a vector space over $\mathbb{F}$ with dimension $d+1$. A Leonard pair on $V$ is an ordered pair of diagonalizable linear transformations $A: V \to V$ and $A^* : V \to V$, each acting in an irreducible tridiagonal fashion on an eigenbasis for the other one. Let $\{v_i\}_{i=0}^d$ (resp.\ $\{v^*_i\}_{i=0}^d$) be such an eigenbasis for $A$ (resp.\ $A^*$). For $0 \leq i \leq d$ define a linear transformation $E_i : V \to V$ such that $E_i v_i=v_i$ and $E_i v_j =0$ if $j \neq i$ $(0 \leq j \leq d)$. Define $E^*_i : V \to V$ in a similar way. The sequence $��=(A, \{E_i\}_{i=0}^d, A^*, \{E^*_i\}_{i=0}^d)$ is called a Leonard system on $V$ with diameter $d$. With respect to the basis $\{v_i\}_{i=0}^d$, let $\{��_i\}_{i=0}^d$ (resp.\ $\{a^*_i\}_{i=0}^d$) be the diagonal entries of the matrix representing $A$ (resp.\ $A^*$). With respect to the basis $\{v^*_i\}_{i=0}^d$, let $\{��^*_i\}_{i=0}^d$ (resp.\ $\{a_i\}_{i=0}^d$) be the diagonal entries of the matrix representing $A^*$ (resp.\ $A$). It is known that $\{��_i\}_{i=0}^d$ (resp. $\{��^*_i\}_{i=0}^d$) are mutually distinct, and the expressions $(��_{i-1}-��_{i+2})/(��_i-��_{i+1})$, $(��^*_{i-1}-��^*_{i+2})/(��^*_i - ��^*_{i+1})$ are equal and independent of $i$ for $1 \leq i \leq d-2$. Write this common value as $��+ 1$. In the present paper we consider the "end-entries" $��_0$, $��_d$, $��^*_0$, $��^*_d$, $a_0$, $a_d$, $a^*_0$, $a^*_d$. We prove that a Leonard system with diameter $d$ is determined up to isomorphism by its end-entries and $��$ if and only if either (i) $��\neq \pm 2$ and $q^{d-1} \neq -1$, where $��=q+q^{-1}$, or (ii) $��= \pm 2$ and $\text{Char}(\mathbb{F}) \neq 2$.
arXiv admin note: substantial text overlap with arXiv:1408.2180
Orthogonal polynomials and functions of hypergeometric type (Jacobi, Laguerre, Hermite, Askey scheme, etc.), Basic orthogonal polynomials and functions (Askey-Wilson polynomials, etc.), tridiagonal pair, Rings and Algebras (math.RA), Leonard pair, Linear transformations, semilinear transformations, FOS: Mathematics, Association schemes, strongly regular graphs, Mathematics - Rings and Algebras, tridiagonal matrix
Orthogonal polynomials and functions of hypergeometric type (Jacobi, Laguerre, Hermite, Askey scheme, etc.), Basic orthogonal polynomials and functions (Askey-Wilson polynomials, etc.), tridiagonal pair, Rings and Algebras (math.RA), Leonard pair, Linear transformations, semilinear transformations, FOS: Mathematics, Association schemes, strongly regular graphs, Mathematics - Rings and Algebras, tridiagonal matrix
| selected citations These citations are derived from selected sources. This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically). | 0 | |
| popularity This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network. | Average | |
| influence This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically). | Average | |
| impulse This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network. | Average |
