Ara es mostren els items 1-20 de 93

    • A description of auto-fixed subgroups in a free group 

      Martino, Armando; Ventura Capell, Enric (2004-06)
      Article
      Accés obert
      Let F be a finitely generated free group. By using Bestvina-Handel theory, as well as some further improvements, the eigengroups of a given automorphism of F (and its fixed subgroup among them) are globally analyzed and ...
    • A lower bound for the size of a Minkowski sum of dilates 

      Hamidoune, Yahya Ould; Rué Perna, Juan José (2011-03-01)
      Article
      Accés obert
      Let A be a finite non-empty set of integers. An asymptotic estimate of the size of the sum of several dilates was obtained by Bukh. The unique known exact bound concerns the sum |A + k·A|, where k is a prime and |A| is ...
    • A note on the degree sequences of graphs with restrictions 

      Muntaner Batle, Francesc Antoni; Rius Font, Miquel (2008-01-15)
      Article
      Accés obert
      Degree sequences of some types of graphs will be studied and characterized in this paper.
    • A recursive presentation for Mihailova's subgroup 

      Bogopolski, Oleg; Ventura Capell, Enric (2010)
      Article
      Accés obert
      We give an explicit recursive presentation for Mihailova's sub- group M(H) of Fn Fn corresponding to a nite, concise and Pei er aspherical presentation H = hx1; : : : ; xn jR1; : : : ;Rmi. This partially answers a ...
    • A solution to the tennis ball problem 

      Mier Vinué, Anna de; Noy Serrano, Marcos (2005)
      Article
      Accés obert
      We present a complete solution to the so-called tennis ball problem, which is equivalent to counting the number of lattice paths in the plane that use North and East steps and lie between certain boundaries. The solution ...
    • A Whitehad algorithm for toral relatively hyperbolic groups 

      Kharlampovich, Olga; Ventura Capell, Enric (2012-12-04)
      Article
      Accés obert
      The Whitehead problem is solved in the class of toral relatively hyperbolic groups G (i.e. torsion-free relatively hyperbolic groups with abelian parabolic subgroups): there is an algorithm which, given two nite ...
    • Absolute type shaft encoding using LFSR sequences with prescribed length 

      Fuertes Armengol, José Mª; Balle, Borja; Ventura Capell, Enric (2006-02)
      Article
      Accés obert
      Maximal-length binary sequences have been known for a long time. They have many interesting properties, one of them is that when taken in blocks of n consecutive positions they form 2 n ° 1 diÆerent codes in a ...
    • Absolute-type shaft encoding using LFSR sequences with a prescribed length 

      Fuertes Armengol, José Mª; Balle Pigem, Borja de; Ventura Capell, Enric (2008-03-31)
      Article
      Accés obert
      Maximal-length binary sequences have existed for a long time. They have many interesting properties, and one of them is that, when taken in blocks of n consecutive positions, they form 2n - 1 different codes in a closed ...
    • Algorithmic problems for free-abelian times free groups 

      Delgado Rodríguez, Jordi; Ventura Capell, Enric (2013-10-01)
      Article
      Accés obert
      We study direct products of free-abelian and free groups with special emphasis on algorithmic problems. After giving natural extensions of standard notions into that family, we find an explicit expression for an arbitrary ...
    • Algorithmic recognition of infinite cyclic extensions 

      Cavallo, Bren; Delgado Rodríguez, Jordi; Kahrobaei, Delaram; Ventura Capell, Enric (2016-10-25)
      Article
      Accés obert
      We prove that one cannot algorithmically decide whether a finitely presented Z-extension admits a finitely generated base group, and we use this fact to prove the undecidability of the BNS invariant. Furthermore, we show ...
    • An algorithm to design prescribed length codes for single-tracked shaft encoders 

      Balle Pigem, Borja de; Ventura Capell, Enric; Fuertes Armengol, José Mª (2009-04-14)
      Text en actes de congrés
      Accés obert
      Abstract-Maximal-length binary shift register sequences have been known for a long time. They have many interesting properties, one of them is that when taken in blocks of n consecutive positions they form 2n - 1 different ...
    • An explicit construction for neighborly centrally symmetric polytopes 

      Pfeifle, Julián (2006-06-29)
      Article
      Accés obert
      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 ...
    • An involution on bicubic maps and beta(0,1)-trees 

      Claesson, Anders; Kitaev, Sergey; Mier Vinué, Anna de (2015)
      Article
      Accés obert
      Bicubic maps are in bijection with (0 ; 1)-trees. We introduce two new ways of decomposing (0 ; 1)-trees. Using this we de ne an endofunc- tion on (0 ; 1)-trees, and thus also on bicubic maps. We show that ...
    • Asymptotic enumeration of non-crossing partitions on surfaces 

      Rué Perna, Juan José; Sau, Ignasi; Thilikos Touloupas, Dimitrios (2013-03-01)
      Article
      Accés obert
      We generalize the notion of non-crossing partition on a disk to general surfaces with boundary. For this, we consider a surface S and introduce the number CS(n) of noncrossing partitions of a set of n points laying on the ...
    • Asymptotic study of subcritical graph classes 

      Drmota, Michael; Fusy, Éric; Kang, Mihyun; Kraus, Veronika; Rué Perna, Juan José (2011-12-01)
      Article
      Accés obert
      We present a unified general method for the asymptotic study of graphs from the so-called subcritical graph classes, which include the classes of cacti graphs, outerplanar graphs, and series-parallel graphs. This general ...
    • Basis expansions and roots of Ehrhart polynomials 

      Pfeifle, Julián; Beck, Matthias; Loera, Jesús de; Develin, Mike; Richard, Stanley (2004)
      Article
      Accés obert
    • Bijections for Baxter families and related objects 

      Felsner, Stefan; Fusy, Éric; Noy Serrano, Marcos; Orden, David (2011-04)
      Article
      Accés obert
      The Baxter number can be written as $B_n = \sum_0^n \Theta_{k,n-k-1}$. These numbers have first appeared in the enumeration of so-called Baxter permutations; $B_n$ is the number of Baxter permutations of size $n$, and ...
    • Bounding the gap between a free group (outer) automorphism and its inverse 

      Ladra, Manuel; Silva, Pedro V.; Ventura Capell, Enric (2016-09-01)
      Article
      Accés obert
      For any finitely generated group GG , two complexity functions aGaG and ßGßG are defined to measure the maximal possible gap between the norm of an automorphism (respectively, outer automorphism) of GG and the norm ...
    • Bounding the volume of facet-empty lattice tetrahedra 

      Pfeifle, Julián; Duong, Han; Haase, Christian; Reznick, Bruce (2005)
      Article
      Accés obert
    • 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)
      Text en actes de congrés
      Accés obert
      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 ...