 
Summary: The Computational Power of Population Protocols
Dana Angluin
Yale University
James Aspnes
Yale University
David Eisenstat
Princeton University
Eric Ruppert
York University
July 27, 2007
Abstract
We consider the model of population protocols introduced by Angluin et al. [AAD+
04], in which
anonymous finitestate agents stably compute a predicate of the multiset of their inputs via twoway
interactions in the family of allpairs communication networks. We prove that all predicates stably
computable in this model (and certain generalizations of it) are semilinear, answering a central open
question about the power of the model. Removing the assumption of twoway interaction, we also
consider several variants of the model in which agents communicate by anonymous messagepassing
where the recipient of each message is chosen by an adversary and the sender is not identified to the
recipient. These oneway models are distinguished by whether messages are delivered immediately or
