Now showing items 1-20 of 21

  • An explicit construction for neighborly centrally symmetric polytopes 

    Pfeifle, Julián (2006-06-29)
    Article
    Open Access
    We give an explicit construction, based on Hadamard matrices, for an infinite series of $\big\lfloor\frac12\sqrt{d}\big\rfloor$-neighborly centrally symmetric $d$-dimensional polytopes with $4d$~vertices. This ...
  • Basis expansions and roots of Ehrhart polynomials 

    Pfeifle, Julián; Beck, Matthias; Loera, Jesús de; Develin, Mike; Richard, Stanley (2004)
    Article
    Open Access
  • Bounding the volume of facet-empty lattice tetrahedra 

    Pfeifle, Julián; Duong, Han; Haase, Christian; Reznick, Bruce (2005)
    Article
    Open Access
  • Búsqueda de comunidades en grafos grandes mediante configuraciones implícitas de vectores 

    Muntés Mulero, Víctor; Padrol Sureda, Arnau; Perarnau Llobet, Guillem; Pfeifle, Julián (PUBL. UNIVERSIDAD DE ZARAGOZA, 2009)
    Conference report
    Open Access
    Presentamos el algoritmo OCA para buscar comunidades solapadas en grafos grandes, como por ejemplo la Wikipedia con 1,6×107 nodos y 1,8×108 aristas. OCA se basa en la búsqueda iterativa de subconjuntos localmente óptimos ...
  • CÀLCUL (Examen 1r quadrimestre, 1r parcial) 

    Pfeifle, Julián (Universitat Politècnica de Catalunya, 2017-11-03)
    Exam
    Restricted access to the UPC academic community
  • Complejos de homomorfismos y disecciones de polígonos 

    Pfeifle, Julián (Secretariado de Publicaciones. Universidad de Valladolid., 2006)
    Conference lecture
    Open Access
    Encontramos realizaciones canónicas de los complejos politopales Hom(G,H)formados por homomorfismos de grafos y estudiados por Babson y Kozlov. Si G es un grafo completo, caracterizamos en qué casos cierta proyección ...
  • Continuous symmetry and shape measures 

    Perarnau Llobet, Guillem; Pfeifle, Julián; Saludes Closa, Jordi (Centre de Recerca Matemàtica, 2010-06)
    Part of book or chapter of book
    Open Access
  • Dissections, Hom-complexes and the Cayley trick 

    Pfeifle, Julián (2006-06-27)
    Article
    Open Access
    We show that certain canonical realizations of the complexes $\Hom(G,H)$ and $\Hom_+(G,H)$ of (partial) graph homomorphisms studied by Babson and Kozlov are in fact instances of the polyhedral Cayley trick. For $G$~a ...
  • Exploiting symmetry on the Universal Polytope 

    Pfeifle, Julián (2012)
    Conference report
    Restricted access - publisher's policy
    The most successful method to date for finding lower bounds on the number of simplices needed to triangulate a given polytope P involves optimizing a linear functional over the associated Universal Polytope U(P). However, ...
  • Gale duality bounds on the location of roots of polynomials with nonnegative coefficients 

    Pfeifle, Julián (2010-04)
    Article
    Open Access
    We bound the location of roots of polynomials that have nonnegative coefficients with respect to a fixed but arbitrary basis of the vector space of polynomials of degree at most d. For this, we interpret the basis polynomials ...
  • Graph operations and Laplacian eigenpolytopes 

    Padrol Sureda, Arnau; Pfeifle, Julián (2010-07)
    Conference report
    Open Access
    We introduce the Laplacian eigenpolytopes ("L-polytopes") associated to a simple undirected graph G, investigate how they change under basic operations such as taking the union, join, complement, line graph and cartesian ...
  • Kalai's squeezed 3-spheres are polytopal 

    Pfeifle, Julián (2002)
    Article
    Open Access
    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
    Open Access
    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 ...
  • MÈTODES MATEMÀTICS III (Examen 1r quadrimestre, 2n parcial) 

    Pfeifle, Julián (Universitat Politècnica de Catalunya, 2016-01-11)
    Exam
    Restricted access to the UPC academic community
  • On polytopality of Cartesian products of graphs 

    Pfeifle, Julián; Pilaud, Vincent; Santos Pérez, Francisco Javier (2010-07)
    Conference report
    Open Access
    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
    Open Access
    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)
    Conference report
    Open Access
    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
    Open Access
    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 ...
  • Prodsimplicial-neighborly polytopes 

    Matschke, Benjamin; Pfeifle, Julián; Pilaud, Vincent (2010-11)
    Article
    Open Access
    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
    Open Access
    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 ...