[Theory Seminar] Yasamin Nazari

December 4, 2019 @ 12:00 pm – 1:00 pm

Speaker: Yasamin Nazari
Affiliation: Johns Hopkins University

Title: Sparse Hopsets in Congested Clique


We give the first Congested Clique algorithm that computes a sparse hopset with polylogarithmic hopbound in polylogarithmic time. Given a graph G=(V,E), a (β,ϵ)-hopset H with “hopbound” β, is a set of edges added to G such that for any pair of nodes u and v in G there is a path with at most β hops in GH with length within (1+ϵ) of the shortest path between u and v in G.
Our hopsets are significantly sparser than the recent construction of Censor-Hillel et al. [6], that constructs a hopset of size Õ (n^{3/2}), but with a smaller polylogarithmic hopbound. On the other hand, the previously known constructions of sparse hopsets with polylogarithmic hopbound in the Congested Clique model, proposed by Elkin and Neiman [10],[11],[12], all require polynomial rounds.
One tool that we use is an efficient algorithm that constructs an -limited neighborhood cover, that may be of independent interest.
Finally, as a side result, we also give a hopset construction in a variant of the low-memory Massively Parallel Computation model, with improved running time over existing algorithms.