The Art Gallery Guardian

Reconstructing edge-disjoint paths, a tighter analysis


This is a small improvement of the analysis of [1], this assume you already read that paper.

Problem1

Given a simple undirected graph of vertices and edges, construct a data structure such that we can query two vertices and , and it returns the maximum edge disjoint paths between and .

We let to be the time to compute -maximum flow on a undirected unit capacity graph.

The current state of art in the article is:

  1. Proprocessing time .
  2. space.
  3. query time.

We can improve this by having a tighter analysis.

First, if and be -edge disjoint path from to and to respectively. Let be the number of edges in , then there exist an algorithm to output -edge disjoint path from to in time. One can see this by update section of their paper by using a stable matching algorithm without the dummy edges, because this is just stable matching with incomplete lists[2].

Second, acyclic flow of value uses only edges(Theorem 3.1 in [3]), therefore we do not have to store any non-acyclic flows. This also speed up all computations because the number of edges are smaller.

Third, we can use space and get a query time of . In fact there is a time space trade off [4].

Thus finally, we get

  1. Proprocessing time .
  2. space.
  3. query time.

With even better analysis, we can obtain the following [5].

  1. Proprocessing time .
  2. space.
  3. query time for a edge disjoint path from to .

References

[1]
M. Conforti, R. Hassin, R. Ravi, Reconstructing edge-disjoint paths, Operations Research Letters. 31 (2003) 273–276 10.1016/S0167-6377(03)00022-1.
[2]
K. Iwama, S. Miyazaki, Y. Morita, D. Manlove, Stable marriage with incomplete lists and ties, in: J. Wiedermann, P. van Emde Boas, M. Nielsen (Eds.), Automata, Languages and Programming, Springer Berlin Heidelberg, 1999: pp. 443–452 10.1007/3-540-48523-6_41.
[3]
D.R. Karger, M.S. Levine, Finding maximum flows in undirected graphs seems easier than bipartite matching, Proceedings of the Thirtieth Annual ACM Symposium on Theory of Computing - STOC ’98. (1998) 69–78 10.1145/276698.276714.
[4]
N. Alon, B. Schieber, Optimal preprocessing for answering on-line product queries, Tel Aviv University, 1987.
[5]
C. Xu, Reconstructing edge-disjoint paths faster, Operations Research Letters. 44 (2016) 174–176 https://doi.org/10.1016/j.orl.2015.12.017.
Posted by Chao Xu on .
Tags: combinatorial optimization.