用大集合查询突破非自适应聚类的查询瓶颈,显著降低所需查询次数。
Clustering with Non-adaptive Subset Queries
- 引入大于2个点的集合查询,通过统计交集簇数获取信息。
- 首个非自适应算法仅需O(n log k · (log k + log log n)²)次查询。
- 适用于并行场景,且对查询大小有约束时仍保持高效。
通过询问集合中属于多少个簇的非自适应子集查询来恢复一个包含n个点的集合U的k-聚类结构,近年来受到广泛关注。以往的成对查询方法在非自适应情况下至少需要Ω(n²)次查询,无法突破二次瓶颈。本文首次提出非自适应的子集查询聚类算法:当|S|>2时,查询返回交集的簇数量。我们设计出一种算法,仅需O(n log k · (log k + log log n)²)次查询,当k为常数时可优化至O(n log log n)。此外,考虑查询大小上限s,证明下界为Ω(max(n²/s², n)),并给出对应上界:当s ≤ √n时为~O(n²k/s²),当s ≤ n时为~O(n²/s)。进一步,在簇大小均衡或允许两轮自适应的情况下,获得更优上界。
原文摘要 · Abstract (English)
Recovering the underlying $k$-clustering of a set $U$ of $n$ points by asking pair-wise same-cluster queries has garnered significant interest in the past few years. Given a query $S \subset U$, $|S|=2$, the oracle returns "yes" if the points are in the same cluster and "no" otherwise. For adaptive algorithms, the query complexity is known to be $Θ(nk)$, while non-adaptive algorithms are extremely limited: even for $k=3$, such algorithms require $Ω(n^2)$ queries, matching the trivial upper bound. However, non-adaptivity is highly desirable since it allows queries to be asked in parallel. To break the quadratic barrier for non-adaptive queries, we study a natural generalization of this problem to subset queries for $|S|>2$, where the oracle returns the number of clusters intersecting $S$. Previous work obtained an $O(n)$ query adaptive algorithm, but the realm of non-adaptive algorithms remained completely unknown. In this paper, we give the first non-adaptive algorithms for clustering with subset queries. Our main result is a non-adaptive algorithm making $O(n \log k \cdot (\log k + \log\log n)^2)$ queries, improving to $O(n \log \log n)$ when $k$ is constant. In addition to non-adaptivity, we make other practical considerations, such as enforcing a bound, $s$, on the query size. We show $Ω(\max(n^2/s^2,n))$ queries are necessary and obtain algorithms making $\smash{\widetilde{O}(n^2k/s^2)}$ queries for any $s \leq \sqrt{n}$ and $\smash{\widetilde{O}(n^2/s)}$ queries for any $s \leq n$. Finally, we obtain improved upper bounds when the clusters are roughly balanced, and when the algorithm is allowed two rounds of adaptivity.
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