On the oriented chromatic index of oriented graphs

On the oriented chromatic index of oriented graphs

A homomorphism from an oriented graph G to an oriented graph H is a mapping φ from the set of vertices of G to the set of vertices of H such that −−−−−−→ φ(u)φ(v) is an arc in H whenever −→ uv is an arc in G. The oriented chromatic index of an oriented graph G is the minimum number of vertices in an oriented graph H such that there exists a homomorphism from the line digraph LD(G) of G to H (th...

the impact of portfolio assessment on iranian efl students essay writing: a process-oriented approach

this study was conducted to investigate the impact of portfolio assessment as a process-oriented assessment mechanism on iranian efl students’ english writing and its subskills of focus, elaboration, organization, conventions, and vocabulary. out of ninety juniors majoring in english literature and translation at the university of isfahan, sixty one of them who were at the same level of writing...

The chromatic number of oriented graphs

On the oriented chromatic number of graphs with given excess

The excess of a graph G is defined as the minimum number of edges that must be deleted from G in order to get a forest. We prove that every graph with excess at most k has chromatic number at most 1 2(3+ √ 1 + 8k) and that this bound is tight. Moreover, we prove that the oriented chromatic number of any graph with excess k is at most k+3, except for graphs having excess 1 and containing a direc...

Acyclic and oriented chromatic numbers of graphs

The oriented chromatic number χo(~ G) of an oriented graph ~ G = (V,A) is the minimum number of vertices in an oriented graph ~ H for which there exists a homomorphism of ~ G to ~ H. The oriented chromatic number χo(G) of an undirected graph G is the maximum of the oriented chromatic numbers of all the orientations of G. This paper discusses the relation between the oriented chromatic number an...