The Euclidean k-means problem is arguably the most widely-studied clustering problem in machine learning. While the k-means objective is NP-hard in the worst-case, practitioners have enjoyed remarkable success in applying heuristics like Lloyd's algorithm for this problem. To address this disconnect, we study the following question: what properties of real-world instances will enable us to design efficient algorithms and prove guarantees for finding the optimal clustering? We consider a natural notion called additive perturbation stability that we believe captures many practical instances. Stable instances have unique optimal k-means solutions that do not change even when each point is perturbed a little (in Euclidean distance). This captures the property that the k-means optimal solution should be tolerant to measurement errors and uncertainty in the points. We design efficient algorithms that provably recover the optimal clustering for instances that are additive perturbation stable. When the instance has some additional separation, we show an efficient algorithm with provable guarantees that is also robust to outliers. We complement these results by studying the amount of stability in real datasets and demonstrating that our algorithm performs well on these benchmark datasets.

本文研究在实际应用中，哪些加性扰动稳定性的实例可以设计有效算法，并证明它们能找到最优聚类。我们提出了一种稳定性定义，并设计了算法以证明稳定实例的最优聚类。当实例具有一定的分离性时，我们显示出一种具有证明保证的鲁棒算法，也能容忍异常值。通过研究真实数据集的稳定性，我们补充了这些结果，并展示了我们的算法在这些基准数据集上的表现。

欧几里得 k-means 的稳定实例聚类