证明了计算VC维的算法下界,并给出基于图结构参数的高效算法。
The Parameterized Complexity of Computing the VC-Dimension
- 在指数时间假设下,原生算法已是渐近最优。
- 首次给出最大度数参数下的1-加性近似算法。
- 适用于图结构的推广问题,效率远超同类方法。
VC维是集合系统(或超图)的核心复杂度度量,广泛应用于机器学习。本文证明:对于超图 $\\(mathcal{H}=(\\(mathcal{V},\\(mathcal{E})$,其计算的朴素 $2^{\\(mathcal{O}(|\\(mathcal{V}|)}$ 时间算法在指数时间假设(ETH)下已渐近最优。进一步证明,当以最大度数为参数时,问题存在1-加性固定参数近似算法;当以维度为参数时,存在固定参数算法,且这些是唯一可利用的结构参数。最后,将问题推广至图结构,设计出针对任意图 $G=(V,E)$ 的 $2^{\\(mathcal{O}(\ m{tw}\cdot \log \ m{tw})}\\(cdot |V|$ 时间算法,其中 $\ m{tw}$ 为树宽(对集合系统即其关联图的树宽)。该结果与相关问题需双指数依赖树宽形成鲜明对比(在ETH假设下)。
原文摘要 · Abstract (English)
The VC-dimension is a well-studied and fundamental complexity measure of a set system (or hypergraph) that is central to many areas of machine learning. We establish several new results on the complexity of computing the VC-dimension. In particular, given a hypergraph $\mathcal{H}=(\mathcal{V},\mathcal{E})$, we prove that the naive $2^{\mathcal{O}(|\mathcal{V}|)}$-time algorithm is asymptotically tight under the Exponential Time Hypothesis (ETH). We then prove that the problem admits a $1$-additive fixed-parameter approximation algorithm when parameterized by the maximum degree of $\mathcal{H}$ and a fixed-parameter algorithm when parameterized by its dimension, and that these are essentially the only such exploitable structural parameters. Lastly, we consider a generalization of the problem, formulated using graphs, which captures the VC-dimension of both set systems and graphs. We design a $2^{\mathcal{O}(\rm{tw}\cdot \log \rm{tw})}\cdot |V|$-time algorithm for any graph $G=(V,E)$ of treewidth $\rm{tw}$ (which, for a set system, applies to the treewidth of its incidence graph). This is in contrast with closely related problems that require a double-exponential dependency on the treewidth (assuming the ETH).
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