Constant-to-one and onto global maps of homomorphisms between strongly connected graphs

Homomorphisms of graphs and their global maps

Homomorphisms of Strongly Regular Graphs

We prove that if G and H are primitive strongly regular graphs with the same parameters and φ is a homomorphism from G to H, then φ is either an isomorphism or a coloring (homomorphism to a complete subgraph). Moreover, any such coloring is optimal for G and its image is a maximum clique of H. Therefore, the only endomorphisms of a primitive strongly regular graph are automorphisms or colorings...

Making Bidirected Graphs Strongly Connected

We consider problems to make a given bidirected graph strongly connected with minimum cardinality of additional signs or additional arcs. For the former problem, we show the minimum number of additional signs and give a linear-time algorithm for finding an optimal solution. For the latter problem, we give a linear-time algorithm for finding a feasible solution whose size is equal to the obvious...

Flipping in Acyclic and Strongly Connected Graphs

A flippable edge in an acyclic digraph is an edge whose reorientation leaves the graph acyclic. We characterize the spanning trees T of an undirected graph G such that there exists an acyclic orientation of G whose set of flippable edges is T . In particular for every edge e ∈ E(G) we give a linear algorithm returning an acyclic orientation and a spanning tree T containing e such that T is the ...

the relationship between field-related cognitive styles and global reading comprehension of hypertext

this study investigates the relationship between field-related cognitive styles and global reading comprehension of hypertext. technically, field dependency is prevailing dominance of field on perception of parts, while global comprehension is skim-like reading to grasp the general content. in this research project, 60 senior and junior students of arak university majoring in english literature...