,
Amin Coja-Oghlan
,
Oliver Gebhard
,
Max Hahn-Klimroth
,
Dominik Kaaser
,
Malin Rau
Creative Commons Attribution 4.0 International license
We study the consensus problem among n agents, defined as follows. Initially, each agent holds one of two possible opinions. The goal is to reach a consensus configuration in which every agent shares the same opinion. To this end, agents randomly sample other agents and update their opinion according to a simple update function depending on the sampled opinions. We consider two communication models: the gossip model and a variant of the population model. In the gossip model, agents are activated in parallel, synchronous rounds. In the population model, one agent is activated after the other in a sequence of discrete time steps. For both models we analyze the following natural family of majority processes called j-Majority: when activated, every agent samples j other agents uniformly at random (with replacement) and adopts the majority opinion among the sample (breaking ties uniformly at random). As our main result we show a hierarchy among majority protocols: (j+1)-Majority (for j > 1) converges stochastically faster than j-Majority for any initial opinion configuration. In our analysis we use Strassen’s Theorem to prove the existence of a coupling. This gives an affirmative answer for the case of two opinions to an open question asked by Berenbrink et al. [PODC 2017].
@InProceedings{berenbrink_et_al:LIPIcs.OPODIS.2022.23,
author = {Berenbrink, Petra and Coja-Oghlan, Amin and Gebhard, Oliver and Hahn-Klimroth, Max and Kaaser, Dominik and Rau, Malin},
title = {{On the Hierarchy of Distributed Majority Protocols}},
booktitle = {26th International Conference on Principles of Distributed Systems (OPODIS 2022)},
pages = {23:1--23:19},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-265-5},
ISSN = {1868-8969},
year = {2023},
volume = {253},
editor = {Hillel, Eshcar and Palmieri, Roberto and Rivi\`{e}re, Etienne},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2022.23},
URN = {urn:nbn:de:0030-drops-176434},
doi = {10.4230/LIPIcs.OPODIS.2022.23},
annote = {Keywords: Consensus, Majority, Hierarchy, Stochastic Dominance, Population Protocols, Gossip Model, Strassen’s Theorem}
}