Tangent circle graphs and 'orders'

  • Authors:
  • Moncef Abbas;Marc Pirlot;Philippe Vincke

  • Affiliations:
  • USTHB, Faculté de Mathématiques, LAID3, BP32, El-Alia, Alger, Algeria;Faculté Polytechnique de Mons, 9 rue de Houdain, B-7000 Mons, Belgium;Université Libre de Bruxelles, CP 210/01, Bd. du Triomphe, B-1050 Bruxelles, Belgium

  • Venue:
  • Discrete Applied Mathematics
  • Year:
  • 2007

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Abstract

Consider a horizontal line in the plane and let @c(A) be a collection of n circles, possibly of different sizes all tangent to the line on the same side. We define the tangent circle graph associated to @c(A) as the intersection graph of the circles. We also define an irreflexive and asymmetric binary relation P on A; the pair (a,b) representing two circles of @c(A) is in P iff the circle associated to a lies to the right of the circle associated to b and does not intersect it. This defines a new nontransitive preference structure that generalizes the semi-order structure. We study its properties and relationships with other well-known order structures, provide a numerical representation and establish a sufficient condition implying that P is transitive. The tangent circle preference structure offers a geometric interpretation of a model of preference relations defined by means of a numerical representation with multiplicative threshold; this representation has appeared in several recently published papers.