In this paper we introduce the notion of an idempotent system. This linear algebraic object is motivated by the structure of an association scheme. We focus on a family of idempotent systems, said to be symmetric. A symmetric idempotent system is an abstraction of the primary module for the subconstituent algebra of a symmetric association scheme. We describe the symmetric idempotent systems in detail. We also consider a class of symmetric idempotent systems, said to be -polynomial and -polynomial. In the topic of orthogonal polynomials there is an object called a Leonard system. We show that a Leonard system is essentially the same thing as a symmetric idempotent system that is -polynomial and -polynomial.
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Keywords: idempotent system, association scheme, Leonard pair
Nomura, Kazumasa 1 ; Terwilliger, Paul 2
CC-BY 4.0
@article{ALCO_2021__4_2_329_0,
author = {Nomura, Kazumasa and Terwilliger, Paul},
title = {Idempotent systems},
journal = {Algebraic Combinatorics},
pages = {329--357},
year = {2021},
publisher = {MathOA foundation},
volume = {4},
number = {2},
doi = {10.5802/alco.159},
language = {en},
url = {http://geodesic.mathdoc.fr/articles/10.5802/alco.159/}
}
Nomura, Kazumasa; Terwilliger, Paul. Idempotent systems. Algebraic Combinatorics, Tome 4 (2021) no. 2, pp. 329-357. doi: 10.5802/alco.159
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