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Kernels in the closure of coloured digraphs

100%

Galeana-Sánchez H., García-Ruvalcaba J.

Discussiones Mathematicae Graph Theory

2000

tom 20

nr 2

243-254

Let D be a digraph with V(D) and A(D) the sets of vertices and arcs of D, respectively. A kernel of D is a set I ⊂ V(D) such that no arc of D joins two vertices of I and for each x ∈ V(D)∖I there is a vertex y ∈ I such that (x,y) ∈ A(D). A digraph is kernel-perfect if every non-empty induced subdigraph of D has a kernel. If D is edge coloured, we define the closure ξ(D) of D the multidigraph with V(ξ(D)) = V(D) and $A(ξ(D)) = ⋃_i{(u,v)$ with colour i there exists a monochromatic path of colour i from the vertex u to the vertex v contained in D}. Let T₃ and C₃ denote the transitive tournament of order 3 and the 3-cycle, respectively, both of whose arcs are coloured with 3 different colours. In this paper, we survey sufficient conditions for the existence of kernels in the closure of edge coloured digraphs, also we prove that if D is obtained from an edge coloured tournament by deleting one arc and D does not contain T₃ or C₃, then ξ(D) is a kernel-perfect digraph.

On graphs all of whose {C₃,T₃}-free arc colorations are kernel-perfect

100%

Galeana-Sánchez H., García-Ruvalcaba J.

Discussiones Mathematicae Graph Theory

2001

tom 21

nr 1

77-93

A digraph D is called a kernel-perfect digraph or KP-digraph when every induced subdigraph of D has a kernel. We call the digraph D an m-coloured digraph if the arcs of D are coloured with m distinct colours. A path P is monochromatic in D if all of its arcs are coloured alike in D. The closure of D, denoted by ζ(D), is the m-coloured digraph defined as follows: V( ζ(D)) = V(D), and A( ζ(D)) = ∪_{i} {(u,v) with colour i: there exists a monochromatic path of colour i from the vertex u to the vertex v contained in D}. We will denoted by T₃ and C₃, the transitive tournament of order 3 and the 3-directed-cycle respectively; both of whose arcs are coloured with three different colours. Let G be a simple graph. By an m-orientation-coloration of G we mean an m-coloured digraph which is an asymmetric orientation of G. By the class E we mean the set of all the simple graphs G that for any m-orientation-coloration D without C₃ or T₃, we have that ζ(D) is a KP-digraph. In this paper we prove that if G is a hamiltonian graph of class E, then its complement has at most one nontrivial component, and this component is K₃ or a star.

Ograniczanie wyników

2 Discussiones Mathematicae Graph Theory

2 Galeana-Sánchez H.

2 García-Ruvalcaba J.

1 2001

1 2000

Wyniki wyszukiwania

Kernels in the closure of coloured digraphs

On graphs all of whose {C₃,T₃}-free arc colorations are kernel-perfect