The Bergman complex of a matroid and phylogenetic trees

  • Authors:
  • Federico Ardila;Caroline J. Klivans

  • Affiliations:
  • Department of Mathematics, University of Washington, Seattle, WA and Mathematical Sciences Research Institute, Berkeley, CA;Departments of Mathematics and Computer Science, University of Chicago, Chicago, IL and Mathematical Sciences Research Institute, Berkeley, CA

  • Venue:
  • Journal of Combinatorial Theory Series B
  • Year:
  • 2006

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Abstract

We study the Bergman complex B(M) of a matroid M: a polyhedral complex which arises in algebraic geometry, but which we describe purely combinatorially. We prove that a natural subdivision of the Bergman complex of M is a geometric realization of the order complex of the proper part of its lattice of flats. In addition, we show that the Bergman fan B˜(Kn) of the graphical matroid of the complete graph Kn is homeomorphic to the space of phylogenetic trees Tn × R. This leads to a proof that the link of the origin in Tn is homeomorphic to the order complex of the proper part of the partition lattice Πn.