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Optimal edge ranking of trees in polynomial time. (English) Zbl 0826.68093
Summary: An edge ranking of a graph is a labeling of the edges using positive integers such that all paths between two edges with the same label contain an intermediate edge with a higher label. An edge ranking is optimal if the highest label used is as small as possible. The edge- ranking problem has applications in scheduling the manufacture of complex multipart products; it is equivalent to finding the minimum height edge- separator tree. In this paper we give the first polynomial-time algorithm to find an optimal edge ranking of a tree, placing the problem in $${\mathcal P}$$. An interesting feature of the algorithm is an usual greedy procedure that allows us to narrow an exponential search space down to a polynomial search space containing an optimal solution. An $${\mathcal {NC}}$$ algorithm is presented that finds an optimal edge ranking for trees for constant degree. We also prove that a natural decision problem emerging from our sequential algorithm is $${\mathcal P}$$-complete.

##### MSC:
 68R10 Graph theory (including graph drawing) in computer science 68M20 Performance evaluation, queueing, and scheduling in the context of computer systems
##### Keywords:
edge ranking; height edge-separator tree; trees
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##### References:
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