On the complete digraphs which are simply disconnected.
Homotopic methods are employed for the characterization of the complete digraphs which are the composition of non-trivial highly regular tournaments.
On the Complexity of the 3-Kernel Problem in Some Classes of Digraphs
Let D be a digraph with the vertex set V (D) and the arc set A(D). A subset N of V (D) is k-independent if for every pair of vertices u, v ∈ N, we have d(u, v), d(v, u) ≥ k; it is l-absorbent if for every u ∈ V (D) − N there exists v ∈ N such that d(u, v) ≤ l. A k-kernel of D is a k-independent and (k − 1)-absorbent subset of V (D). A 2-kernel is called a kernel. It is known that the problem of determining whether a digraph has a kernel (“the kernel problem”) is NP-complete, even in quite restricted...
On the decomposition of complete directed graphs into factors with given radii
On the Decomposition of the Complete Directed Graph into Factors with Given Diameters
On The Determinant of q-Distance Matrix of a Graph
In this note, we show how the determinant of the q-distance matrix Dq(T) of a weighted directed graph G can be expressed in terms of the corresponding determinants for the blocks of G, and thus generalize the results obtained by Graham et al. [R.L. Graham, A.J. Hoffman and H. Hosoya, On the distance matrix of a directed graph, J. Graph Theory 1 (1977) 85-88]. Further, by means of the result, we determine the determinant of the q-distance matrix of the graph obtained from a connected weighted graph...
On the dichromatic number in kernel theory
On the Domination of Cartesian Product of Directed Cycles: Results for Certain Equivalence Classes of Lengths
Let (−→ Cm2−→ Cn) be the domination number of the Cartesian product of directed cycles −→ Cm and −→ Cn for m, n ≥ 2. Shaheen [13] and Liu et al. ([11], [12]) determined the value of (−→ Cm2−→ Cn) when m ≤ 6 and [12] when both m and n ≡ 0(mod 3). In this article we give, in general, the value of (−→ Cm2−→ Cn) when m ≡ 2(mod 3) and improve the known lower bounds for most of the remaining cases. We also disprove the conjectured formula for the case m ≡ 0(mod 3) appearing in [12].
On the Existence of (k,l)-Kernels in Infinite Digraphs: A Survey
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, 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) set of vertices. A k-kernel is a (k, k −1)-kernel. This work is a survey of results proving sufficient conditions for the existence of (k, l)-kernels in infinite digraphs. Despite all the previous work in this direction was done for...
On the exponent of -regular primitive matrices.
On the heights of power digraphs modulo
A power digraph, denoted by , is a directed graph with as the set of vertices and as the edge set. In this paper we extend the work done by Lawrence Somer and Michal Křížek: On a connection of number theory with graph theory, Czech. Math. J. 54 (2004), 465–485, and Lawrence Somer and Michal Křížek: Structure of digraphs associated with quadratic congruences with composite moduli, Discrete Math. 306 (2006), 2174–2185. The heights of the vertices and the components of for and are determined....
On the heterochromatic number of circulant digraphs
The heterochromatic number hc(D) of a digraph D, is the minimum integer k such that for every partition of V(D) into k classes, there is a cyclic triangle whose three vertices belong to different classes. For any two integers s and n with 1 ≤ s ≤ n, let be the oriented graph such that is the set of integers mod 2n+1 and In this paper we prove that for n ≥ 7. The bound is tight since equality holds when s ∈ n,[(2n+1)/3].
On the Hypercompetition Numbers of Hypergraphs with Maximum Degree at Most Two
In this note, we give an easy and short proof for the theorem by Park and Kim stating that the hypercompetition numbers of hypergraphs with maximum degree at most two is at most two.
On the intersection graph of a commutative distributive groupoid
On the lattice of convex subsets of a partial monounary algebra
On the -basis of a digraph
On the Maximum Eigenvalue of a Reducible Non-Negative Real Matrix.
On the maximum number of arcs in some classes of graphs
On the monotone upper bound problem.
On the normal disconnection of a tree
On the number of complete subgraphs and circuits contained in graphs