نتایج جستجو برای: singlesource digraph

تعداد نتایج: 2553  

Journal: :European Journal of Combinatorics 2014

Journal: :Linear Algebra and its Applications 2013

Journal: :Revue française d'automatique informatique recherche opérationnelle. Mathématique 1973

Journal: :Discussiones Mathematicae Graph Theory 2012
César Hernández-Cruz

Let D be a digraph, V (D) and A(D) will denote the sets of vertices and arcs of D, respectively. A digraph D is 3-transitive if the existence of the directed path (u, v, w, x) of length 3 in D implies the existence of the arc (u, x) ∈ A(D). In this article strong 3-transitive digraphs are characterized and the structure of non-strong 3-transitive digraphs is described. The results are used, e.g...

Journal: :SIAM J. Matrix Analysis Applications 2003
Simone Severini

Given a matrix M of size n, the digraph D on n vertices is said to be the digraph of M , when Mij 6= 0 if and only if (vi, vj) is an arc of D. We give a necessary condition, called strong quadrangularity, for a digraph to be the digraph of a unitary matrix. With the use of such a condition, we show that a line digraph, − → L D, is the digraph of a unitary matrix if and only if D is Eulerian. It...

Journal: :Discrete Mathematics 2012
César Hernández-Cruz Hortensia Galeana-Sánchez

Let D be a digraph, V (D) and A(D) will denote the sets of vertices and arcs of D, respectively. A (k, l)-kernel N of D is a k-independent (if u, v ∈ N then d(u, v), d(v, u) ≥ k) and l-absorbent (if u ∈ V (D) − N then there exists v ∈ N such that d(u, v) ≤ l) set of vertices. A k-kernel is a (k, k − 1)-kernel. A digraph D is transitive if (u, v), (v, w) ∈ A(D) implies that (u,w) ∈ A(D). This co...

2017
C. Dalfó M. A. Fiol M. Miller J. Ryan

We study the relationship between two key concepts in the theory of digraphs, those of quotient digraphs and voltage digraphs. These techniques contract or expand a given digraph in order to study its characteristics, or obtain more involved structures. As an application, we relate the spectrum of a digraph Γ, called voltage digraph or base, with the spectrum of its lifted digraph Γ. We prove t...

Journal: :Journal of Graph Theory 2008
Daniela Kühn Deryk Osthus Andrew Young

Mader conjectured that for all ` there is an integer δ(`) such that every digraph of minimum outdegree at least δ(`) contains a subdivision of a transitive tournament of order `. In this note we observe that if the minimum outdegree of a digraph is sufficiently large compared to its order then one can even guarantee a subdivision of a large complete digraph. More precisely, let ~ G be a digraph...

Journal: :Discussiones Mathematicae Graph Theory 2011
Hortensia Galeana-Sánchez César Hernández-Cruz

Let D be a digraph, V (D) and A(D) will denote the sets of vertices and arcs of D, respectively. A (k, l)-kernel N of D is a k-independent set of vertices (if u, v ∈ N , u 6= v, then d(u, v), d(v, u) ≥ k) and l-absorbent (if u ∈ V (D) − N then there exists v ∈ N such that d(u, v) ≤ l). A k-kernel is a (k, k − 1)-kernel. Quasi-transitive, right-pretransitive and left-pretransitive digraphs are g...

2012
Anil Kumar Parameswaran Ashok Nair

In this paper we introduce the Cayley digraph structure. This can be considered as a generalization of Cayley digraph. We prove that all Cayley digraph structures are vertex transitive. Many graph theoretic properties are studied in terms of algebraic properties.

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