Equational theories of tropical semirings

  • Authors:
  • Luca Aceto;Zoltán Ésik;Anna Ingólfsdóttir

  • Affiliations:
  • BRICS (Basic Research in Computer Science), Centre of the Danish National Research Foundation, Department of Computer Science, Aalborg University, Ft. Bajersvej 7E, 9220 Aalborg ø, Denmark;Department of Computer Science, University of Szeged, Árpád tér 2, 6720 Szeged, Hungary;deCODE Genetics, Sturlugata 8, 101 Reykjavik, Iceland

  • Venue:
  • Theoretical Computer Science - Foundations of software science and computation structures
  • Year:
  • 2003

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Abstract

This paper studies the equational theories of various exotic semirings presented in the literature. Exotic semirings are semirings whose underlying carrier set is some subset of the set of real numbers equipped with binary operations of minimum or maximum as sum, and addition as product. Two prime examples of such structures are the (max,+) semiring and the tropical semiring. It is shown that none of the exotic semirings commonly considered in the literature has a finite basis for its equations, and that similar results hold for the commutative idempotent weak semirings that underlie them. For each of these commutative idempotent weak semirings, the paper offers characterizations of the equations that hold in them, decidability results for their equational theories, explicit descriptions of the free algebras in the varieties they generate, and relative axiomatization results.