Now showing items 1-20 of 22

    • 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
    • DISCRETE AND ALGORITHMIC GEOMETRY | FINAL 

      Pfeifle, Julián (Universitat Politècnica de Catalunya, 2019-01-10)
      Exam
      Restricted access to the UPC academic community
    • 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 ...