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| Content Provider | ACM Digital Library |
|---|---|
| Author | Khanna, Sanjeev Chekuri, Chandra |
| Copyright Year | 2007 |
| Abstract | The approximability of the maximum edge-disjoint paths problem (EDP) in directed graphs was seemingly settled by an $Ω(m^{1/2}$ ™ &epsis;)-hardness result of Guruswami et al. [2003], and an $\textit{O}(&sqrt;\textit{m})$ approximation achievable via a natural multicommodity-flow-based LP relaxation as well as a greedy algorithm. Here $\textit{m}$ is the number of edges in the graph. We observe that the $Ω(m^{1/2}$ ™ &epsis;)-hardness of approximation applies to $\textit{sparse}$ graphs, and hence when expressed as a function of $\textit{n},$ that is, the number of vertices, only an $Ω(n^{1/2}™$ &epsis;)-hardness follows. On the other hand, $\textit{O}(&sqrt;\textit{m})-approximation$ algorithms do not guarantee a $\textit{sublinear}$ (in terms of $\textit{n})$ approximation algorithm for $\textit{dense}$ graphs. We note that a similar gap exists in the known results on the integrality gap of the flow-based LP relaxation: an $Ω(&sqrt;\textit{n})$ lower bound and $\textit{O}(&sqrt;\textit{m})$ upper bound. Motivated by this discrepancy in the upper and lower bounds, we study algorithms for EDP in directed and undirected graphs and obtain improved approximation ratios. We show that the greedy algorithm has an approximation ratio of $O(min(n^{2/3},$ $&sqrt;\textit{m}))$ in undirected graphs and a ratio of $O(min(n^{4/5},$ $&sqrt;\textit{m}))$ in directed graphs. For acyclic graphs we give an $\textit{O}(&sqrt;\textit{n}$ ln $\textit{n})$ approximation via LP rounding. These are the first sublinear approximation ratios for EDP. The results also extend to EDP with weights and to the uniform-capacity unsplittable flow problem (UCUFP). |
| File Format | |
| ISSN | 15496325 |
| e-ISSN | 15496333 |
| DOI | 10.1145/1290672.1290683 |
| Volume Number | 3 |
| Issue Number | 4 |
| Journal | ACM Transactions on Algorithms (TALG) |
| Language | English |
| Publisher | Association for Computing Machinery (ACM) |
| Publisher Date | 2007-11-01 |
| Publisher Place | New York |
| Access Restriction | One Nation One Subscription (ONOS) |
| Subject Keyword | Edge-disjoint paths Approximation algorithm Greedy algorithm Multicommodity flow relaxation |
| Content Type | Text |
| Resource Type | Article |
| Subject | Mathematics |
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