Clustering in the Boolean hypercube in a list decoding regime

We consider the following clustering with outliers problem: Given a set of points X ⊂ {-1,1}ⁿ, such that there is some point z ∈ {-1,1}ⁿ for which Pr_x∈X[〈x,z〉 ≥ ε] ≥ δ, find z. We call such a point z a (δ,ε)-center of X. In this work we give lower and upper bounds for the task of finding a (δ,ε)-center. We first show that for δ = 1 - ν close to 1, i.e. in the "unique decoding regime", given a (1 - ν,ε)-centered set our algorithm can find a (1 - (1 + o(1))ν,(1 - o(1))ε)-center. More interestingly, we study the "list decoding regime", i.e. when δ is close to 0. Our main upper bound shows that for values of ε and δ that are larger than 1/polylog(n), there exists a polynomial time algorithm that finds a (δ - o(1),ε - o(1))-center. Moreover, our algorithm outputs a list of centers explaining all of the clusters in the input. Our main lower bound shows that given a set for which there exists a (δ,ε)-center, it is hard to find even a (δ/n^c, ε)-center for some constant c and ε = 1/poly(n), δ = 1/poly(n).