Recent Submissions

  • 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 ...
  • Lower bounds on the maximum number of non-crossing acyclic graphs 

    Huemer, Clemens; Mier Vinué, Anna de (2015-08-01)
    Article
    Restricted access - publisher's policy
    This paper is a contribution to the problem of counting geometric graphs on point sets. More concretely, we look at the maximum numbers of non-crossing spanning trees and forests. We show that the so-called double chain ...
  • Finite automata for Schreier graphs of virtually free groups 

    Silva, Pedro V.; Soler Escrivà, Xaro; Ventura Capell, Enric (2016-01-01)
    Article
    Restricted access - publisher's policy
    The Stallings construction for f.g. subgroups of free groups is generalized by introducing the concept of Stallings section, which allows efficient computation of the core of a Schreier graph based on edge folding. It is ...
  • On the probability of planarity of a random graph near the critical point 

    Noy Serrano, Marcos; Ravelomanana, Vlady; Rue, Juanjo (2015-03-01)
    Article
    Open Access
    Let G(n, M) be the uniform random graph with n vertices and M edges. Erdos and Renyi (1960) conjectured that the limiting probability; lim(n ->infinity) Pr{G(n, n/2) is planar}; exists and is a constant strictly between 0 ...
  • The conjugacy problem for free-by-cyclic groups 

    Martino, Armando; Ventura Capell, Enric (2004-04)
    External research report
    Open Access
    We show that the conjugacy problem is solvable in [finitely generated free]-by-cyclic groups, by using a result of O. Maslakova that one can algorithmically find generating sets for the fixed sub- groups of free group ...
  • The automorphism group of a free-by-cyclic group in rank 2 

    Bogopolski, Oleg; Martino, Armando; Ventura Capell, Enric (2007-05)
    Article
    Open Access
    Let ¡ be an automorphism of a free group F 2 of rank 2 and let M ¡ = F 2 o ¡ Z be the corresponding mapping torus of ¡ . We prove that the group Out ( M ¡ ) is usually virtually cyclic. More- over, ...
  • 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
    Open Access
    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 ...
  • Absolute type shaft encoding using LFSR sequences with prescribed length 

    Fuertes Armengol, José Mª; Balle, Borja; Ventura Capell, Enric (2006-02)
    Article
    Open Access
    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 ...
  • Completion and decomposition of a clutter into representable matroids 

    Martí Farré, Jaume; Mier Vinué, Anna de (Elsevier, 2015-05-01)
    Article
    Restricted access - publisher's policy
    This paper deals with the question of completing a monotone increasing family of subsets Gamma of a finite set Omega to obtain the linearly dependent subsets of a family of vectors of a vector space. Specifically, we prove ...
  • Fixed subgroups are compressed in surface groups 

    Zhang, Qiang; Ventura Capell, Enric; Wu, Jianchun (2015-08-01)
    Article
    Restricted access - publisher's policy
    For a compact surface Sigma (orientable or not, and with boundary or not), we show that the fixed subgroup, Fix B, of any family B of endomorphisms of pi(1)(Sigma) is compressed in pi(1)(Sigma), i.e. rk(Fix B) <= rk(H) for ...

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