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Population Protocols with Unordered Data

Authors Michael Blondin , François Ladouceur

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Author Details

Michael Blondin
  • Department of Computer Science, Université de Sherbrooke, Canada
François Ladouceur
  • Department of Computer Science, Université de Sherbrooke, Canada


We thank Manuel Lafond for his ideas and feedback in the early phase of our research. We further thank the anonymous reviewers for their comments and insightful suggestions.

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Michael Blondin and François Ladouceur. Population Protocols with Unordered Data. In 50th International Colloquium on Automata, Languages, and Programming (ICALP 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 261, pp. 115:1-115:20, Schloss Dagstuhl - Leibniz-Zentrum für Informatik (2023)


Population protocols form a well-established model of computation of passively mobile anonymous agents with constant-size memory. It is well known that population protocols compute Presburger-definable predicates, such as absolute majority and counting predicates. In this work, we initiate the study of population protocols operating over arbitrarily large data domains. More precisely, we introduce population protocols with unordered data as a formalism to reason about anonymous crowd computing over unordered sequences of data. We first show that it is possible to determine whether an unordered sequence from an infinite data domain has a datum with absolute majority. We then establish the expressive power of the "immediate observation" restriction of our model, namely where, in each interaction, an agent observes another agent who is unaware of the interaction.

Subject Classification

ACM Subject Classification
  • Theory of computation → Distributed computing models
  • Theory of computation → Automata over infinite objects
  • Population protocols
  • unordered data
  • colored Petri nets


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