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arXiv 1001.2891cs.DS
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检测高对数密度--Denmark-子图的O(n^1/4)逼近

Detecting High Log-Densities -- an O(n^1/4) Approximation for Densest k-Subgraph

Aditya Bhaskara, Moses Charikar, Eden Chlamtac, Uriel Feige, Aravindan Vijayaraghavan

摘要:

在Denk-Subgraph问题中,给定一个图G和一个参数k,人们需要找到一个在k个顶点上导出的G的子图,该子图包含最多的边。在这个问题的最著名的上界和下界之间有一个很大的差距。它是NP难的,并且没有PTAS,除非NP有次指数时间算法。另一方面,Feige、Kortsarz和Peleg的当前最著名的算法对于某些特定的ε> 0(估计在1/60左右)给出了n^(1/3-ε)的近似比。我们提出了一个算法,对于每个n> 0近似Denk-Subgraph问题的比率为n^(1/4+ n)在时间n^O(1/n)。特别是,我们的算法在时间n^O(log n)上实现了O(n^1/4)的近似比。我们的算法的灵感来自于研究一个平均情况下的版本的问题,其目标是区分随机图与种植密集的子图。我们在一般情况下获得的近似比与我们在这个种植问题中获得的区分比相匹配。在一个高层次上,我们的算法涉及巧妙地计数适当定义的树G中的恒定大小,并使用这些计数来识别稠密子图的顶点。我们的算法基于以下原则。如果图G(V,E)的平均度为Theta(|V| ^alpha),则称图G(V,E)具有对数密度α。我们的结果的算法的核心是一个家庭的算法,输出k-子图的非平凡密度的对数密度的denominik-子图是大于对数密度的主机图。

英文摘要:

In the Densest k-Subgraph problem, given a graph G and a parameter k, one needs to find a subgraph of G induced on k vertices that contains the largest number of edges. There is a significant gap between the best known upper and lower bounds for this problem. It is NP-hard, and does not have a PTAS unless NP has subexponential time algorithms. On the other hand, the current best known algorithm of Feige, Kortsarz and Peleg, gives an approximation ratio of n^(1/3-epsilon) for some specific epsilon > 0 (estimated at around 1/60). We present an algorithm that for every epsilon > 0 approximates the Densest k-Subgraph problem within a ratio of n^(1/4+epsilon) in time n^O(1/epsilon). In particular, our algorithm achieves an approximation ratio of O(n^1/4) in time n^O(log n). Our algorithm is inspired by studying an average-case version of the problem where the goal is to distinguish random graphs from graphs with planted dense subgraphs. The approximation ratio we achieve for the general case matches the distinguishing ratio we obtain for this planted problem. At a high level, our algorithms involve cleverly counting appropriately defined trees of constant size in G, and using these counts to identify the vertices of the dense subgraph. Our algorithm is based on the following principle. We say that a graph G(V,E) has log-density alpha if its average degree is Theta(|V|^alpha). The algorithmic core of our result is a family of algorithms that output k-subgraphs of nontrivial density whenever the log-density of the densest k-subgraph is larger than the log-density of the host graph.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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