论文标题

关于几何独立集和集团的流算法

On Streaming Algorithms for Geometric Independent Set and Clique

论文作者

Bhore, Sujoy, Klute, Fabian, Oostveen, Jelle J.

论文摘要

我们研究流模型中最大的几何独立集和集团问题。给定仅在插入流中到达的几何对象的集合,其目的是找到一个子集,以使子集中的所有对象分别均不连接或相交。 我们表明,没有使用线性数量的位数,没有恒定因子近似算法来找到最大的独立段或$ 2 $ - 室间。有趣的是,我们的证明只需要一组相交图也是间隔图的段。这揭示了细分之间和间隔之间的有趣差异,因为确实存在$ 2 $ - approximation,以找到仅使用$ o(α(\ nathcal {i})\ log | \ nog | \ nogcal {i} |)$的内存记忆的独立间隔集,用于一组间隔$ \ mathcal $ \ mathcal {i} $) $ \ Mathcal {i} $的最大独立集。另一方面,我们表明,对于几何集团问题,即使对于单位间隔,也没有使用小于线性的位的恒定因素近似算法。从积极方面来看,我们表明,在一组与轴对准的单位矩形中的最大几何独立集可以仅使用$ o(α(\ Mathcal {r})\ log | \ log | \ Mathcal {r} |)$ bits仅使用$ 4 $ approximation。

We study the maximum geometric independent set and clique problems in the streaming model. Given a collection of geometric objects arriving in an insertion only stream, the aim is to find a subset such that all objects in the subset are pairwise disjoint or intersect respectively. We show that no constant factor approximation algorithm exists to find a maximum set of independent segments or $2$-intervals without using a linear number of bits. Interestingly, our proof only requires a set of segments whose intersection graph is also an interval graph. This reveals an interesting discrepancy between segments and intervals as there does exist a $2$-approximation for finding an independent set of intervals that uses only $O(α(\mathcal{I})\log |\mathcal{I}|)$ bits of memory for a set of intervals $\mathcal{I}$ with $α(\mathcal{I})$ being the size of the largest independent set of $\mathcal{I}$. On the flipside we show that for the geometric clique problem there is no constant-factor approximation algorithm using less than a linear number of bits even for unit intervals. On the positive side we show that the maximum geometric independent set in a set of axis-aligned unit-height rectangles can be $4$-approximated using only $O(α(\mathcal{R})\log |\mathcal{R}|)$ bits.

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