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arXiv 1107.1052cs.DScs.CCcs.DM
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三次和次三次图上的旅行商问题

The traveling salesman problem on cubic and subcubic graphs

Sylvia Boyd, René Sitters, Suzanne van der Ster, Leen Stougie

摘要:

研究了三次图和次三次图的度量完备化问题,该问题是NP-难的。这个问题是有趣的,因为它与著名的度量TSP的4/3猜想有关,该猜想说,完整性间隙,即,TSP的最优值与其线性规划松弛(subtour elimination relaxation)之间的最差情况比为4/3。我们提出了近似比为4/3的三次图的第一个算法。证明使用多面体技术在一个令人惊讶的方式,这是独立的利益。事实上,我们建设性地证明了,对于任何三次图的$n$顶点的旅游长度为4n/3 - 2存在,这也意味着4/3猜想,作为一个上界,这类图TSP。最近,Mömke和Svensson提出了一个随机算法,给出了一般图上图-TSP的1.461-近似,并作为副结果给出了次三次图上图-TSP的4/3-近似算法,解决了这类图-TSP的4/3猜想.我们将提出一种方法去随机化他们的算法,导致一个更小的运行时间比明显的去随机化。所有后者也适用于多重图。

英文摘要:

We study the Travelling Salesman Problem (TSP) on the metric completion of cubic and subcubic graphs, which is known to be NP-hard. The problem is of interest because of its relation to the famous 4/3 conjecture for metric TSP, which says that the integrality gap, i.e., the worst case ratio between the optimal values of the TSP and its linear programming relaxation (the subtour elimination relaxation), is 4/3. We present the first algorithm for cubic graphs with approximation ratio 4/3. The proof uses polyhedral techniques in a surprising way, which is of independent interest. In fact we prove constructively that for any cubic graph on $n$ vertices a tour of length 4n/3-2 exists, which also implies the 4/3 conjecture, as an upper bound, for this class of graph-TSP. Recently, Mömke and Svensson presented a randomized algorithm that gives a 1.461-approximation for graph-TSP on general graphs and as a side result a 4/3-approximation algorithm for this problem on subcubic graphs, also settling the 4/3 conjecture for this class of graph-TSP. We will present a way to derandomize their algorithm which leads to a smaller running time than the obvious derandomization. All of the latter also works for multi-graphs.

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