Ara es mostren els items 14-26 de 26

    • Kalai's squeezed 3-spheres are polytopal 

      Pfeifle, Julián (2002)
      Article
      Accés obert
      In 1988, Kalai [5] extended a construction of Billera and Lee to produce many triangulated(d−1)-spheres. In fact, in view of upper bounds on the number of simplicial d-polytopes by Goodman and Pollack [2, 3], he derived ...
    • Kalai's squeezed three-spheres are polytopal 

      Pfeifle, Julián (2001)
      Article
      Accés obert
      In 1988, Kalai [5] extended a construction of Billera and Lee to produce many triangulated(d−1)-spheres. In fact, in view of upper bounds on the number of simplicial d-polytopes by Goodman and Pollack [2,3], he derived ...
    • Large final polynomials from integer programming 

      Pfeifle, Julián (2021-09)
      Article
      Accés obert
      We introduce a new method for finding a non-realizability certificate of a simplicial sphere S. It enables us to prove for the first time the non-realizability of a balanced 2-neighborly 3-sphere by Zheng, a family of ...
    • MÈTODES MATEMÀTICS III (Examen 1r quadrimestre, 2n parcial) 

      Pfeifle, Julián (Universitat Politècnica de Catalunya, 2016-01-11)
      Examen
      Accés restringit a la comunitat UPC
    • On polytopality of Cartesian products of graphs 

      Pfeifle, Julián; Pilaud, Vincent; Santos Pérez, Francisco Javier (2010-07)
      Text en actes de congrés
      Accés obert
      We study the polytopality of Cartesian products of non-polytopal graphs. On the one hand, we prove that a product of graphs is the graph of a simple polytope if and only if its factors are. On the other hand, we provide ...
    • On the monotone upper bound problem 

      Pfeifle, Julián; Ziegler, Günter M. (2004)
      Article
      Accés obert
      The Monotone Upper Bound Problem asks for the maximal number M(d,n) of vertices on a strictly-increasing edge-path on a simple d-polytope with n facets. More specifically, it asks whether the upper bound M(d,n) ≤ ...
    • Overlapping community search for social networks 

      Padrol Sureda, Arnau; Perarnau Llobet, Guillem; Pfeifle, Julián; Muntés Mulero, Víctor (IEEE Press. Institute of Electrical and Electronics Engineers, 2010)
      Text en actes de congrés
      Accés obert
      Finding decompositions of a graph into a family of clusters is crucial to understanding its underlying structure. While most existing approaches focus on partitioning the nodes, real-world datasets suggest the presence ...
    • Polygons as sections of higher-dimensional polytopes 

      Padrol Sureda, Arnau; Pfeifle, Julián (2015-02-09)
      Article
      Accés obert
      We show that every heptagon is a section of a 3-polytope with 6 vertices. This implies that every n-gon with n >= 7 can be obtained as a section of a (2 + [n/7])-dimensional polytope with at most [6n/7] vertices; and ...
    • Positive Plücker tree certificates for non-realizability 

      Pfeifle, Julián (2022-01-24)
      Article
      Accés obert
      We introduce a new method for finding a non-realizability certificate of a simplicial sphere S: we exhibit a monomial combination of classical 3-term Pl¨ucker relations that yields a sum of products of determinants that ...
    • Prodsimplicial-neighborly polytopes 

      Matschke, Benjamin; Pfeifle, Julián; Pilaud, Vincent (2010-11)
      Article
      Accés obert
      We introduce PSN polytopes whose k-skeleton is combinatorially equivalent to that of a product of r simplices. They simultaneously generalize both neighborly and neighborly cubical polytopes. We construct PSN polytopes ...
    • Root polytopes and growth series of root lattices 

      Ardila, Federico; Beck, Matthias; Hosten, Serkan; Pfeifle, Julián; Seashore, Kim (2011)
      Article
      Accés obert
      The convex hull of the roots of a classical root lattice is called a root polytope. We determine explicit unimodular triangulations of the boundaries of the root polytopes associated to the root lattices $A_n$, $C_n$, and ...
    • Showing non-realizability of spheres by distilling a tree 

      Pfeifle, Julián (2021)
      Text en actes de congrés
      Accés obert
      In [Zhe20a], Hailun Zheng constructs a combinatorial 3-sphere on 16 vertices whose graph is the complete 4-partite graph K4;4;4;4. Such a sphere seems unlikely to be realizable as the boundary complex of a 4-dimensional ...
    • The rotation graph of k-ary trees is Hamiltonian 

      Huemer, Clemens; Hurtado Díaz, Fernando Alfredo; Pfeifle, Julián (Crete University Press, 2006)
      Article
      Accés restringit per política de l'editorial
      In this paper we show that the graph of k-ary trees, connected by rotations, contains a Hamilton cycle. Our proof is constructive and thus provides a cyclic Gray code for k-ary trees. Furthermore, we identify a basic ...