Distance-regular graphs, pseudo primitive idempotents, and the Terwilliger algebra
نویسندگان
چکیده
منابع مشابه
Distance-regular graphs, pseudo primitive idempotents, and the Terwilliger algebra
Let Γ denote a distance-regular graph with diameter D ≥ 3, intersection numbers ai, bi, ci and Bose-Mesner algebra M. For θ ∈ C ∪∞ we define a 1 dimensional subspace of M which we call M(θ). If θ ∈ C then M(θ) consists of those Y in M such that (A−θI)Y ∈ CAD, where A (resp. AD) is the adjacency matrix (resp. Dth distance matrix) of Γ. If θ = ∞ then M(θ) = CAD. By a pseudo primitive idempotent f...
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In this paper, we prove the following two theorems. Theorem 1 Let 0 denote a distance-regular graph with diameter d ≥ 3. Suppose E and F are primitive idempotents of 0, with cosine sequences σ0, σ1, . . . , σd and ρ0, ρ1, . . . , ρd , respectively. Then the following are equivalent. (i) The entry-wise product E ◦ F is a scalar multiple of a primitive idempotent of 0. (ii) There exists a real nu...
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ژورنال
عنوان ژورنال: European Journal of Combinatorics
سال: 2004
ISSN: 0195-6698
DOI: 10.1016/s0195-6698(03)00114-8