Now showing items 21-30 of 30

    • IconOn an inequivalence criterion for cocyclic Hadamard matrices  [Article]

      Armario Sampalo, José Andrés (Springer, 2010)
      Given two Hadamard matrices of the same order, it can be quite difficult to decide whether or not they are equivalent. There are some criteria to determine Hadamard inequivalence. Among them, one of the most commonly ...
    • IconOn higher dimensional cocyclic Hadamard matrices  [Article]

      Álvarez Solano, Víctor; Armario Sampalo, José Andrés; Frau García, María Dolores; Real Jurado, Pedro (2015)
      Provided that a cohomological model for G is known, we describe a method for constructing a basis for n-cocycles over G, from which the whole set of n-dimensional n-cocyclic matrices over G may be straightforwardly calculated. ...
    • IconOn quasi-orthogonal cocycles  [Article]

      Armario Sampalo, José Andrés; Flannery, D.L. (Wiley, 2017)
      We introduce the notion of quasi-orthogonal cocycle. This is motivated in part by the maximal determinant problem for square {±1}-matrices of size congruent to 2 modulo 4. Quasi-orthogonal cocycles are analogous to the ...
    • Icon(Pseudo)-cocyclic (structured) Hadamard matrices over (quasi)groups  [Presentation]

      Álvarez Solano, Víctor; Armario Sampalo, José Andrés; Falcón Ganfornina, Raúl Manuel; Frau García, María Dolores; Gudiel Rodríguez, Félix; Güemes Alzaga, María Belén; Kotsireas, Ilias (2017)
      Progressing on a survey of the state of the art of cocyclic constructions for Hadamard matrices, we will prove that the family of Goethals-Seidel Hadamard matrices is (pseudo)-cocyclic over a certain family of quasigroups. ...
    • IconQuasi-Hadamard Full Propelinear Codes  [Article]

      Armario Sampalo, José Andrés; Bailera, Iván; Borges, Joachim; Rifá, Josep (Springer, 2018)
      In this paper, we give a characterization of quasi-Hadamard groups in terms of propelinear codes. We define a new class of codes that we call quasi-Hadamard full propelinear codes. Some structural properties of these ...
    • IconRooted Trees Searching for Cocyclic Hadamard Matrices over D4t  [Presentation]

      Álvarez Solano, Víctor; Armario Sampalo, José Andrés; Frau García, María Dolores; Gudiel Rodríguez, Félix; Osuna Lucena, Amparo (Springer, 2009)
      A new reduction on the size of the search space for cocyclic Hadamard matrices over dihedral groups D4t is described, in terms of the so called central distribution. This new search space adopt the form of a forest ...
    • IconSearching for partial Hadamard matrices  [Presentation]

      Álvarez Solano, Víctor; Armario Sampalo, José Andrés; Frau García, María Dolores; Gudiel Rodríguez, Félix; Güemes Alzaga, María Belén; Martín García, Elena; Osuna Lucena, Amparo (Universidade de Santiago de Compostela, Servicio de Publicaciones, 2010)
      Three algorithms looking for pretty large partial Hadamard ma- trices are described. Here “large” means that hopefully about a third of a Hadamard matrix (which is the best asymptotic result known so far, [8]) is achieved. ...
    • IconSelf-Dual codes from (−1,1)-matrices of skew symmetric type  [Article]

      Armario Sampalo, José Andrés; Frau García, María Dolores (Cornell University, 2013)
      Previously, self-dual codes have been constructed from weighing matrices, and in particular from conference matrices (skew and symmetric). In this paper, codes constructed from matrices of skew symmetric type whose ...
    • IconThe homological reduction method for computing cocyclic Hadamard matrices  [Article]

      Álvarez Solano, Víctor; Armario Sampalo, José Andrés; Frau García, María Dolores; Real Jurado, Pedro (2009)
      An alternate method for constructing (Hadamard) cocyclic matrices over a finite group GG is described. Provided that a homological model View the MathML sourceB̄(Z[G])ϕ:⇌HFhG for GG is known, the homological reduction ...
    • IconTransferring TTP-structures via contraction  [Article]

      Frau García, María Dolores; Real Jurado, Pedro; Armario Sampalo, José Andrés; Álvarez Solano, Víctor (2005)