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Computing a clique tree with algorithm MLS (Maximal Label Search)

Algorithm MLS (Maximal Label Search) is a graph search algorithm which generalizes algorithms MCS, LexBFS, LexDFS and MNS. On a chordal graph, MLS computes a peo (perfect elimination ordering) of the graph. We show how algorithm MLS can be modified to compute a pmo (perfect moplex ordering) as well as a clique tree and the minimal separators of a chordal graph. We give a necessary and sufficient condition on the labeling structure for the beginning of a new clique in the clique tree to be detected by a condition on labels. MLS is also used to compute a clique tree of the complement graph, and new cliques in the complement graph can be detected by a condition on labels for any labeling structure. A linear time algorithm computing a pmo and the generators of the maximal cliques and minimal separators w.r.t. this pmo of the complement graph is provided. On a non-chordal graph, algorithm MLSM is used to compute an atom tree of the clique minimal separator decomposition of any graph.