On symmetric association schemes and associated quotient-polynomial graphs
Let denote an undirected, connected, regular graph with vertex set , adjacency matrix , and distinct eigenvalues. Let denote the subalgebra of generated by . We refer to as the adjacency algebra of . In this paper we investigate algebraic and combinatorial structure of for which the adjacency algebr...
| Autores: | , |
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| Tipo de recurso: | artículo |
| Fecha de publicación: | 2021 |
| País: | España |
| Institución: | Universitat Politècnica de Catalunya (UPC) |
| Repositorio: | UPCommons. Portal del coneixement obert de la UPC |
| Idioma: | inglés |
| OAI Identifier: | oai:upcommons.upc.edu:2117/363194 |
| Acceso en línea: | https://hdl.handle.net/2117/363194 https://dx.doi.org/10.5802/ALCO.187 |
| Access Level: | acceso abierto |
| Palabra clave: | Combinatorial analysis Graph theory Symmetric association scheme Adjacency algebra Quotient-polynomial graph Intersection diagram Combinacions (Matemàtica) Grafs, Teoria de Classificació AMS::05 Combinatorics::05E Algebraic combinatorics Classificació AMS::05 Combinatorics::05C Graph theory Àrees temàtiques de la UPC::Matemàtiques i estadística::Matemàtica discreta::Combinatòria Àrees temàtiques de la UPC::Matemàtiques i estadística::Matemàtica discreta::Teoria de grafs |
| Sumario: | Let denote an undirected, connected, regular graph with vertex set , adjacency matrix , and distinct eigenvalues. Let denote the subalgebra of generated by . We refer to as the adjacency algebra of . In this paper we investigate algebraic and combinatorial structure of for which the adjacency algebra is closed under Hadamard multiplication. In particular, under this simple assumption, we show the following: (i) has a standard basis ; (ii) for every vertex there exists identical distance-faithful intersection diagram of with cells; (iii) the graph is quotient-polynomial; and (iv) if we pick then has distinct eigenvalues if and only if . We describe the combinatorial structure of quotient-polynomial graphs with diameter and distinct eigenvalues. As a consequence of the techniques used in the paper, some simple algorithms allow us to decide whether is distance-regular or not and, more generally, which distance- matrices are polynomial in , giving also these polynomials. |
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