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| Content Provider | Society for Industrial and Applied Mathematics (SIAM) |
|---|---|
| Author | Kratsch, Stefan |
| Copyright Year | 2018 |
| Abstract | In the vertex cover problem we are given a graph $G=(V,E)$ and an integer $k$ and have to determine whether there is a set $X\subseteq V$ of size at most $k$ such that each edge in $E$ has at least one endpoint in $X$. The problem can be easily solved in time $\mathcal{O}^*(2^k)$, making it fixed-parameter tractable (FPT) with respect to $k$. While the fastest known algorithm takes only time $\mathcal{O}^*(1.2738^k)$, much stronger improvements have been obtained by studying parameters that are smaller than $k$. Apart from treewidth-related results, the arguably best algorithm for vertex cover runs in time $\mathcal{O}^*(2.3146^p)$, where $p=k-LP(G)$ is only the excess of the solution size $k$ over the best fractional vertex cover [Lokshtanov et al. ACM Trans. Algorithms, 11 (2014), pp. 15:1--15:31]. Since $p\leq k$ but $k$ cannot be bounded in terms of $p$ alone, this strictly increases the range of tractable instances. Recently, [Garg and Philip, Proceedings of the Symposium on Discrete Algorithms, 2016, pp. 1152--1166] greatly contributed to understanding the parameterized complexity of the vertex cover problem. They prove that $2LP(G)-MM(G)$ is a lower bound for the vertex cover size of $G$, where $MM(G)$ is the size of a largest matching of $G$, and proceed to study parameter $\ell=k-(2LP(G)-MM(G))$. They give an algorithm of running time $\mathcal{O}^*(3^\ell)$, proving that vertex cover is FPT in $\ell$. It can be easily observed that $\ell\leq p$ whereas $p$ cannot be bounded in terms of $\ell$ alone. We complement the work of Garg and Philip by proving that vertex cover admits a randomized polynomial kernelization in terms of $\ell$, i.e., an efficient preprocessing to size polynomial in $\ell$. This improves over parameter $p=k-LP(G)$ for which this was previously known [Kratsch and Wahlström, Proceedings of the IEEE Symposium on Foundations of Computer Science, 2012, pp. 450--459]. |
| Starting Page | 1806 |
| Ending Page | 1839 |
| Page Count | 34 |
| File Format | |
| ISSN | 08954801 |
| DOI | 10.1137/16M1104585 |
| e-ISSN | 10957146 |
| Journal | SIAM Journal on Discrete Mathematics (SJDMEC) |
| Issue Number | 3 |
| Volume Number | 32 |
| Language | English |
| Publisher | Society for Industrial and Applied Mathematics |
| Publisher Date | 2018-07-26 |
| Access Restriction | Subscribed |
| Subject Keyword | Nonnumerical algorithms vertex cover parameterized complexity polynomial kernelization Randomized algorithms Analysis of algorithms |
| Content Type | Text |
| Resource Type | Article |
| Subject | Mathematics |
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