Minimal half-spaces and external representation of tropical polyhedra

  • Authors:
  • Stéphane Gaubert;Ricardo D. Katz

  • Affiliations:
  • INRIA and Centre de Mathématiques Appliquées (CMAP), École Polytechnique, Palaiseau Cedex, France 91128;CONICET, Instituto de Matemática "Beppo Levi", Universidad Nacional de Rosario, Rosario, Argentina 2000

  • Venue:
  • Journal of Algebraic Combinatorics: An International Journal
  • Year:
  • 2011

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Abstract

We give a characterization of the minimal tropical half-spaces containing a given tropical polyhedron, from which we derive a counter-example showing that the number of such minimal half-spaces can be infinite, contradicting some statements which appeared in the tropical literature, and disproving a conjecture of F. Block and J. Yu. We also establish an analogue of the Minkowski---Weyl theorem, showing that a tropical polyhedron can be equivalently represented internally (in terms of extreme points and rays) or externally (in terms of half-spaces containing it). A canonical external representation of a polyhedron turns out to be provided by the extreme elements of its tropical polar. We characterize these extreme elements, showing in particular that they are determined by support vectors.