A Γ-design of the complete graph Kv is a set D of subgraphs isomorphic to Γ (blocks) whose edge-sets partition the edge-set of Kv. D is balanced if the number of blocks containing x is the same number of blocks containing y for any two vertices x and y. D is orbit-balanced, or strongly balanced, if the number of blocks containing x as a vertex of a vertex-orbit A of Γ is the same number of blocks containing y as a vertex of A, for any two vertices x and y and for every vertex-orbit A of Γ. We say that D is degree-balanced if the number of blocks containing x as a vertex of degree d in Γ is the same number of blocks containing y as a vertex of degree d in Γ, for any two vertices x and y and for every degree d in Γ. An orbit-balanced Γ-design is also degree-balanced; a degree-balanced Γ-design is also balanced. The converse is not always true. We study the spectrum for orbit-balanced, degree-balanced, and balanced Γ-designs of Kv when Γ is a graph with five vertices, none of which is isolated. We also study the existence of balanced (respectively, degree-balanced) Γ-designs of Kv which are not degree-balanced (respectively, not orbit-balanced).
Degree- and orbit-balanced Γ-designs when Γ has five vertices / Bonvicini, Simona. - In: JOURNAL OF COMBINATORIAL DESIGNS. - ISSN 1063-8539. - STAMPA. - 21:9(2013), pp. 359-389. [10.1002/jcd.21348]
Degree- and orbit-balanced Γ-designs when Γ has five vertices
BONVICINI, Simona
2013
Abstract
A Γ-design of the complete graph Kv is a set D of subgraphs isomorphic to Γ (blocks) whose edge-sets partition the edge-set of Kv. D is balanced if the number of blocks containing x is the same number of blocks containing y for any two vertices x and y. D is orbit-balanced, or strongly balanced, if the number of blocks containing x as a vertex of a vertex-orbit A of Γ is the same number of blocks containing y as a vertex of A, for any two vertices x and y and for every vertex-orbit A of Γ. We say that D is degree-balanced if the number of blocks containing x as a vertex of degree d in Γ is the same number of blocks containing y as a vertex of degree d in Γ, for any two vertices x and y and for every degree d in Γ. An orbit-balanced Γ-design is also degree-balanced; a degree-balanced Γ-design is also balanced. The converse is not always true. We study the spectrum for orbit-balanced, degree-balanced, and balanced Γ-designs of Kv when Γ is a graph with five vertices, none of which is isolated. We also study the existence of balanced (respectively, degree-balanced) Γ-designs of Kv which are not degree-balanced (respectively, not orbit-balanced).File | Dimensione | Formato | |
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