Perturbation Resilient Clustering for k-Center and Related Problems via LP Relaxations

We consider clustering in the perturbation resilience model that has been studied since the work of Bilu and Linial [ICS, 2010] and Awasthi, Blum and Sheffet [Inf. Proc. Lett., 2012]. A clustering instance I is said to be α-perturbation resilient if the optimal solution does not change when the pairwise distances are modified by a factor of α and the perturbed distances satisfy the metric property --- this is the metric perturbation resilience property introduced in Angelidakis et. al. [STOC, 2010] and a weaker requirement than prior models. We make two high-level contributions. 1) We show that the natural LP relaxation of k-center and asymmetric k-center is integral for 2-perturbation resilient instances. We belive that demonstrating the goodness of standard LP relaxations complements existing results that are based on combinatorial algorithms designed for the perturbation model. 2) We define a simple new model of perturbation resilience for clustering with outliers. Using this model we show that the unified MST and dynamic programming based algorithm proposed by Angelidakis et. al. [STOC, 2010] exactly solves the clustering with outliers problem for several common center based objectives (like k-center, k-means, k-median) when the instances is 2-perturbation resilient. We further show that a natural LP relxation is integral for 2-perturbation resilient instances of kcenter with outliers.