Browsing by Author "Pfeifle, Julián"

An explicit construction for neighborly centrally symmetric polytopes
Pfeifle, Julián (20060629)
Article
Open AccessWe 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 facetempty 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 AccessPresentamos 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 ... 
Complejos de homomorfismos y disecciones de polígonos
Pfeifle, Julián (Secretariado de Publicaciones. Universidad de Valladolid., 2006)
Conference lecture
Open AccessEncontramos 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, 201006)
Part of book or chapter of book
Open Access 
Dissections, Homcomplexes and the Cayley trick
Pfeifle, Julián (20060627)
Article
Open AccessWe 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 policyThe 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 (201004)
Article
Open AccessWe 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 (201007)
Conference report
Open AccessWe introduce the Laplacian eigenpolytopes ("Lpolytopes") 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 3spheres are polytopal
Pfeifle, Julián (2002)
Article
Open AccessIn 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 dpolytopes by Goodman and Pollack [2, 3], he derived ... 
Kalai's squeezed threespheres are polytopal
Pfeifle, Julián (2001)
Article
Open AccessIn 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 dpolytopes by Goodman and Pollack [2,3], he derived ... 
On polytopality of Cartesian products of graphs
Pfeifle, Julián; Pilaud, Vincent; Santos Pérez, Francisco Javier (201007)
Conference report
Open AccessWe study the polytopality of Cartesian products of nonpolytopal 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 AccessThe Monotone Upper Bound Problem asks for the maximal number M(d,n) of vertices on a strictlyincreasing edgepath on a simple dpolytope 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 AccessFinding 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, realworld datasets suggest the presence ... 
Polygons as sections of higherdimensional polytopes
Padrol Sureda, Arnau; Pfeifle, Julián (20150209)
Article
Open AccessWe show that every heptagon is a section of a 3polytope with 6 vertices. This implies that every ngon with n >= 7 can be obtained as a section of a (2 + [n/7])dimensional polytope with at most [6n/7] vertices; and ... 
Prodsimplicialneighborly polytopes
Matschke, Benjamin; Pfeifle, Julián; Pilaud, Vincent (201011)
Article
Open AccessWe introduce PSN polytopes whose kskeleton 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 AccessThe 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 ... 
The rotation graph of kary trees is Hamiltonian
Huemer, Clemens; Hurtado Díaz, Fernando Alfredo; Pfeifle, Julián (Crete University Press, 2006)
Article
Restricted access  publisher's policyIn this paper we show that the graph of kary trees, connected by rotations, contains a Hamilton cycle. Our proof is constructive and thus provides a cyclic Gray code for kary trees. Furthermore, we identify a basic ...