English

Some matrices associated with the split decomposition for a Q-polynomial distance-regular graph

Combinatorics 2007-10-25 v1

Abstract

We consider a QQ-polynomial distance-regular graph Γ\Gamma with vertex set XX and diameter D3D \geq 3. For μ,ν{,}\mu, \nu \in \lbrace \downarrow, \uparrow \rbrace we define a direct sum decomposition of the standard module V=\CXV=\C X, called the (μ,ν)(\mu,\nu)--split decomposition. For this decomposition we compute the complex conjugate and transpose of the associated primitive idempotents. Now fix b,βCb,\beta \in \mathbb C such that b1b \neq 1 and assume Γ\Gamma has classical parameters (D,b,α,β)(D,b,\alpha,\beta) with α=b1\alpha = b-1. Under this assumption Ito and Terwilliger displayed an action of the qq-tetrahedron algebra q\boxtimes_q on the standard module of Γ\Gamma. To describe this action they defined eight matrices in MatX(C)\hbox{Mat}_X(\mathbb C), called \begin{eqnarray*} \label{eq:list} A,\quad A^*,\quad B,\quad B^*, \quad K,\quad K^*,\quad \Phi,\quad \Psi. \end{eqnarray*} For each matrix in the above list we compute the transpose and complex conjugate. Using this information we compute the transpose and complex conjugate for each generator of q\boxtimes_q on VV.

Keywords

Cite

@article{arxiv.0710.4383,
  title  = {Some matrices associated with the split decomposition for a Q-polynomial distance-regular graph},
  author = {Joohyung Kim},
  journal= {arXiv preprint arXiv:0710.4383},
  year   = {2007}
}
R2 v1 2026-06-21T09:35:19.917Z