A General Algorithmic Scheme for Modular Decompositions of Hypergraphs and Applications.

We study here algorithmic aspects of modular decomposition of hypergraphs. In the literature one can find three different definitions of modules, namely: the standard one [19], the k-subset modules [6] and the Courcelle's one [11]. Using the fundamental tools defined for combinatorial decompositions such as partitive and orthogonal families, we directly derive a linear time algorithm for Courcelle's decomposition. Then we introduce a general algorithmic tool for partitive families and apply it for the other two definitions of modules to derive polynomial algorithms. For standard modules it leads to an algorithm in O(n(3) center dot l) time (where n is the number of vertices and l is the sum of the size of the edges). For k-subset modules we obtain O(n(3) center dot m center dot l) (where m is the number of edges). This is an improvement from the best known algorithms for k-subset modular decomposition, which was not polynomial w.r.t. n and m, and is in O(n(3k-5)) time [6] where k denotes the maximal size of an edge. Finally we focus on applications of orthogonality to modular decompositions of tournaments, simplifying the algorithm from [18]. The question of designing a linear time algorithms for the standard modular decomposition of hypergraphs remains open.