Now showing items 204-223 of 244

    • Spatio-temporal configurations of human-caused fires in Spain through point patterns 

      Costafreda Aumedes, Sergi; Comas Rodríguez, Carles; Vega García, Cristina (MDPI, 2016)
      Human-caused wildfires are often regarded as unpredictable, but usually occur in patterns aggregated over space and time. We analysed the spatio-temporal configuration of 7790 anthropogenic wildfires (2007–2013) in nine ...
    • Spectra and eigenspaces of arbitrary lifts of graphs 

      Dalfó, Cristina; Fiol, Miguel Angel; Pavlíková, Sona; Sirán, Josef (Faculty of Mathematics, Physics and Informatics, Comenius University, 2019)
      We describe, in a very explicit way, a method for determining the spec-tra and bases of all the corresponding eigenspaces of arbitrary lifts of graphs (regularor not).
    • Sufficient conditions for a digraph to admit a (1,≤ℓ)-identifying code 

      Balbuena, C.; Dalfó, Cristina; Martínez Barona, B. (University of Zielona Góra, 2019)
      A (1, ≤ `)-identifying code in a digraph D is a subset C of vertices of D such that all distinct subsets of vertices of cardinality at most ` have distinct closed in-neighbourhoods within C. In this paper, we give some ...
    • Super edge-magic models 

      López Masip, Susana-Clara; Muntaner Batle, F. A.; Rius Font, Miquel (Springer, 2011)
      In this paper, we generalize the concept of super edge-magic graph by introducing the new concept of super edge-magic models.
    • Synthetic generation of social network data with endorsements 

      Pérez Rosés, Hebert; Sebé Feixas, Francesc (Palgrave Macmillan, 2014)
      In many simulation studies involving networks there is the need to rely on a sample network to perform the simulation experiments. In many cases, real network data is not available due to privacy concerns. In that case we ...
    • The (∆,D) and (∆,N) problems in double-step digraphs with unilateral distance 

      Dalfó, Cristina; Fiol, Miguel Angel (Indonesian Combinatorial Society (InaCombS); Graph Theory and Applications (GTA) Research Centre; University of Newcastle, Australia; Institut Teknologi Bandung (ITB), Indonesia, 2014)
      We study the (Delta,D) and (Delta,N) problems for double-step digraphs considering the unilateral distance, which is the minimum between the distance in the digraph and the distance in its converse digraph, obtained by ...
    • The 2-adic valuation of the cardinality of Jacobians of genus 2 curves over quadratic towers of finite fields 

      Garra Oronich, Ricard; Miret, Josep M. (Josep Maria); Pujolàs Boix, Jordi; Thériault, Nicolas (World Scientific Publishing, 2018)
      Given a genus 2 curve C defined over a finite field Fq of odd characteristic such that 2|#Jac(C)(Fq), we study the growth of the 2-adic valuation of the cardinality of the Jacobian over a tower of quadratic extensions of ...
    • The center problem and composition condition for Abel differential equations 

      Giné, Jaume; Grau Montaña, Maite; Santallusia Esvert, Xavier (Elsevier, 2015)
      The classical Poincaré center-focus problem for planar polynomial systems of ordinary differential equations can be transformed, in certain particular cases, to the center problem of a trigonometric Abel differential ...
    • The center problem for a 2:-3 resonant cubic Lotka–Volterra system 

      Dolićanin, Diana; Giné, Jaume; Oliveira, Regilene; Romanovski, Valery G. (Elsevier, 2013)
      In this paper we obtain conditions on the coefficients of a cubic Lotka–Volterra system of the form equation(1) x=x(2-a20x2-a11xy-a02y2), ẏ=y(-3+b20x2+b11xy+b02y2), which fulfillment yields the existence in a ...
    • The cubic polynomial differential systems with two circles as algebraic limit cycles 

      Giné, Jaume; Llibre, Jaume; Valls, Claudia (Walter de Gruyter GmbH, 2018)
      In this paper we characterize all cubic polynomial differential systems in the plane having two circles as invariant algebraic limit cycles.
    • The cyclicity of polynomial centers via the reduced bautin depth 

      García, I. A. (Isaac A.) (American Mathematical Society, 2016)
      We describe a method for bounding the cyclicity of the class of monodromic singularities of polyn omial planar families of vector fields X λ with an analytic Poincar e first return map having a polynomial Bautin ideal B ...
    • The Degree/Diameter Problem for Mixed Abelian Cayley Graphs 

      López Lorenzo, Ignacio; Pérez Rosés, Hebert; Pujolàs Boix, Jordi (Elsevier, 2017-11-20)
      This paper investigates the upper bounds for the number of vertices in mixed abelian Cayley graphs with given degree and diameter. Additionally, in the case when the undirected degree is equal to one, we give a construction ...
    • The diameter of cyclic Kautz digraphs 

      Böhmová, Katerina; Dalfó, Cristina; Huemer, Clemens (Faculty of Sciences and Mathematics, University of Nis, Serbia, 2017)
      We present a new kind of digraphs, called cyclic Kautz digraphs CK(d, ɭ), which are subdigraphs of the well-known Kautz digraphs K(d,ɭ). The latter have the smallest diameter among all digraphs with their number of ...
    • The Hopf cyclicity of the centers of a class of quintic polynomial vector fields 

      García, I. A. (Isaac A.); Llibre, Jaume; Maza Sabido, Susana (Elsevier, 2015-01-20)
      We consider families of planar polynomial vector fields having a singularity with purely imaginary eigenvalues for which a basis of its Bautin ideal B is known. We provide an algorithm for computing an upper bound of the ...
    • The inverse integrating factor and the Poincaré map 

      García, I. A. (Isaac A.); Giacomini, Héctor; Grau Montaña, Maite (American Mathematical Society, 2010)
      This work is concerned with planar real analytic differential systems with an analytic inverse integrating factor defined in a neighborhood of a regular orbit. We show that the inverse integrating factor defines an ...
    • The jumping knight and other (super) edge-magic constructions 

      López Masip, Susana-Clara; Muntaner Batle, F. A.; Rius Font, Miquel (Springer, 2014)
      Let G be a graph of order p and size q with loops allowed. A bijective function f:V(G)∪E(G)→{i}p+qi=1 is an edge-magic labeling of G if the sum f(u)+f(uv)+f(v)=k is independent of the choice of the edge uv. The constant k ...
    • The Manhattan Product of Digraphs 

      Comellas, Francesc; Dalfó, Cristina; Fiol, Miguel Angel (Indonesian Combinatorial Society (InaCombS); Graph Theory and Applications (GTA) Research Centre; University of Newcastle, Australia; Institut Teknologi Bandung (ITB), Indonesia, 2013)
      We study the main properties of a new product of bipartite digraphs which we call Manhattan product. This product allows us to understand the subjacent product in the Manhattan street networks and can be used to built other ...
    • The null divergence factor 

      Chavarriga Soriano, Javier; Giacomini, Héctor; Giné, Jaume (Universitat Autònoma de Barcelona. Departament de Matemàtiques, 1997)
      Let (P, Q) be a C 1 vector field defined in a open subset U ⊂ R2 . We call a null divergence factor a C 1 solution V (x, y) of the equation P ∂V + Q ∂V = ∂P + ∂Q V . In previous works ∂x ∂y ∂x ∂y it has been ...
    • The power of digraph products applied to labelings 

      Ichishima, R.; López Masip, Susana-Clara; Muntaner Batle, F. A.; Rius Font, Miquel (Elsevier, 2012)
      The ⊗h-product was introduced in 2008 by Figueroa-Centeno et al. as a way to construct new families of (super) edge-magic graphs and to prove that some of those families admit an exponential number of (super) edge-magic ...
    • The problem of distinguishing between a center and a focus for nilpotent and degenerate analytic systems 

      Giacomini, Héctor; Giné, Jaume; Llibre, Jaume (Elsevier, 2006)
      In this work we study the centers of planar analytic vector fields which are limit of linear type centers. It is proved that all the nilpotent centers are limit of linear type centers and consequently the Poincaré–Liapunov ...