Disimplicial arcs, transitive vertices, and disimplicial eliminations

MARTINIANO EGUÍA; FRANCISCO J. SOULIGNAC

DISCRETE MATHEMATICS AND THEORETICAL COMPUTER SCIENCE (DMTCS)

DISCRETE MATHEMATICS THEORETICAL COMPUTER SCIENCE

Lugar: Nancy; Año: 2015 vol. 17 p. 101 - 118

1365-8050

   In this article we deal with the problems of finding the disimplicial arcs of a digraph and recognizing some interesting graph classes defined by their existence.  A emph{diclique} of a digraph is a pair $V o W$ of sets of vertices such that $v o w$ is an arc for every $v in V$ and $w in W$.  An arc $v o w$ is emph{disimplicial} when it belongs to a unique maximal diclique.  We show that the problem of finding the disimplicial arcs is equivalent, in terms of time and space complexity, to that of locating the transitive vertices.  As a result, an efficient algorithm to find the bisimplicial edges of bipartite graphs is obtained.  Then, we develop simple algorithms to build disimplicial elimination schemes, which can be used to generate bisimplicial elimination schemes for bipartite graphs.  Finally, we study two classes related to perfect disimplicial elimination digraphs, namely weakly diclique irreducible digraphs and diclique irreducible digraphs.  The former class is associated to finite posets, while the latter corresponds to dedekind complete finite posets.