For a given graph G we say that a G-design is balanced if there exists a constant r such that for each point x the number of blocks containing x is equal to r. A G-design is degree-balanced if, for each degree d occurring in the graph G, there exists a constant r_d such that, for each point x, the number of blocks containing x as a vertex of degree d is equal to r_d.Let V_1, V_2, . . . , V_h be the vertex-orbits of G under its automorphism group. A G-design is said to be orbit-balanced (or strongly balanced) if for i = 1, 2, . . . , h there exists a constant R_i such that, for each point x the number of blocks of the G-design in which x occurs as an element in the orbit V_i is equal to R_i.If G is a tree with six vertices, we determine the values of v for which a balanced G-design with v points exists, the values of v for which a degree-balanced G-design with v points exists, and the values of v for which an orbit-balanced G-design with v points exists.We also consider the existence problem for G-designs which are not balanced, which are balanced but not degree-balanced, and which are degree-balanced but not orbit-balanced.

Tree-designs with balanced-type conditions / Bonisoli, Arrigo; Ruini, Beatrice. - In: DISCRETE MATHEMATICS. - ISSN 0012-365X. - STAMPA. - 313:(2013), pp. 1197-1205. [10.1016/j.disc.2011.12.020]

### Tree-designs with balanced-type conditions

#### Abstract

For a given graph G we say that a G-design is balanced if there exists a constant r such that for each point x the number of blocks containing x is equal to r. A G-design is degree-balanced if, for each degree d occurring in the graph G, there exists a constant r_d such that, for each point x, the number of blocks containing x as a vertex of degree d is equal to r_d.Let V_1, V_2, . . . , V_h be the vertex-orbits of G under its automorphism group. A G-design is said to be orbit-balanced (or strongly balanced) if for i = 1, 2, . . . , h there exists a constant R_i such that, for each point x the number of blocks of the G-design in which x occurs as an element in the orbit V_i is equal to R_i.If G is a tree with six vertices, we determine the values of v for which a balanced G-design with v points exists, the values of v for which a degree-balanced G-design with v points exists, and the values of v for which an orbit-balanced G-design with v points exists.We also consider the existence problem for G-designs which are not balanced, which are balanced but not degree-balanced, and which are degree-balanced but not orbit-balanced.
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2013
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1197
1205
Tree-designs with balanced-type conditions / Bonisoli, Arrigo; Ruini, Beatrice. - In: DISCRETE MATHEMATICS. - ISSN 0012-365X. - STAMPA. - 313:(2013), pp. 1197-1205. [10.1016/j.disc.2011.12.020]
Bonisoli, Arrigo; Ruini, Beatrice
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Utilizza questo identificativo per citare o creare un link a questo documento: `https://hdl.handle.net/11380/704336`
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