Vertex splitting and the recognition of trapezoid graphs
Trapezoid graphs are the intersection family of trapezoids where every trapezoid has a pair of opposite sides lying on two parallel lines. These graphs have received considerable attention and lie strictly between permutation graphs (where the trapezoids are lines) and cocomparability graphs (the complement has a transitive orientation). The operation of vertex splitting, introduced in (Cheah and Corneil, 1996)[3], first augments a given graph G G and then transforms the augmented graph by replacing each of the original graphs vertices by a pair of new vertices. This splitted graph is a permutation graph with special properties if and only if G G is a trapezoid graph. Recently vertex splitting has been used to show that the recognition problems for both tolerance and bounded tolerance graphs is NP-complete (Mertzios etal., 2010)[11]. Unfortunately, the vertex splitting trapezoid graph recognition algorithm presented in (Cheah and Corneil, 1996)[3] is not correct. In this paper, we present a new way of augmenting the given graph and using vertex splitting such that the resulting algorithm is simpler and faster than the one reported in (Cheah and Corneil, 1996)[3].
vertex splitting recognition trapezoid graphs permutation graphs polynomial algorithm