Department of Computer Science | Institute of Theoretical Computer Science | CADMO

Theory of Combinatorial Algorithms

Prof. Emo Welzl and Prof. Bernd Gärtner

Mittagsseminar (in cooperation with A. Steger, D. Steurer and B. Sudakov)

Mittagsseminar Talk Information

Date and Time: Thursday, September 27, 2018, 12:15 pm

Duration: 30 minutes

Location: OAT S15/S16/S17

Speaker: Jara Uitto

Sparsifying Distributed Algorithms in the Low-Memory Massively Parallel Computation Model

The Massively Parallel Computation (MPC) model serves as a common abstraction of many modern large-scale parallel computation frameworks and has recently gained a lot of importance, especially in the context of classic graph problems. Unfortunately, most of the known efficient MPC algorithms seem to get fundamentally stuck at the linear-memory barrier: their efficiency crucially relies on each machine having space at least linear in the number n of nodes. As this might not only be prohibitively large, but also allows for easy if not trivial solutions for sparse graphs, we are interested in the low-memory MPC model, where the space per machine is restricted to be strongly sublinear, that is, n^d for any 0 < d < 1. We study maximal matching (MM) and maximal independent set (MIS) and introduce a method for "sparsifying" distributed algorithms that, roughly speaking, allows us to run local distributed algorithms without the knowledge of the whole local topology. This, in turn, allows us to speed up the local algorithms using the global communication power of the MPC model without breaking the memory restrictions. In the case of MIS and MM, our method yields algorithms with runtime of O( sqrt(log Delta) ), where Delta is the maximum degree of the input graph. As a by-product, we obtain a 2-approximation for Minimum Vertex Cover, (2 + eps)-approximation for maximum weighted matching, and a (1 + eps)-approximation for maximum cardinality matching without a loss in the overall runtimes.

Upcoming talks     |     All previous talks     |     Talks by speaker     |     Upcoming talks in iCal format (beta version!)

Previous talks by year:   2024  2023  2022  2021  2020  2019  2018  2017  2016  2015  2014  2013  2012  2011  2010  2009  2008  2007  2006  2005  2004  2003  2002  2001  2000  1999  1998  1997  1996  

Information for students and suggested topics for student talks

Automatic MiSe System Software Version 1.4803M   |   admin login