30 research outputs found
Generic method for bijections between blossoming trees and planar maps
This article presents a unified bijective scheme between planar maps and
blossoming trees, where a blossoming tree is defined as a spanning tree of the
map decorated with some dangling half-edges that enable to reconstruct its
faces. Our method generalizes a previous construction of Bernardi by loosening
its conditions of applications so as to include annular maps, that is maps
embedded in the plane with a root face different from the outer face.
The bijective construction presented here relies deeply on the theory of
\alpha-orientations introduced by Felsner, and in particular on the existence
of minimal and accessible orientations. Since most of the families of maps can
be characterized by such orientations, our generic bijective method is proved
to capture as special cases all previously known bijections involving
blossoming trees: for example Eulerian maps, m-Eulerian maps, non separable
maps and simple triangulations and quadrangulations of a k-gon. Moreover, it
also permits to obtain new bijective constructions for bipolar orientations and
d-angulations of girth d of a k-gon.
As for applications, each specialization of the construction translates into
enumerative by-products, either via a closed formula or via a recursive
computational scheme. Besides, for every family of maps described in the paper,
the construction can be implemented in linear time. It yields thus an effective
way to encode and generate planar maps.
In a recent work, Bernardi and Fusy introduced another unified bijective
scheme, we adopt here a different strategy which allows us to capture different
bijections. These two approaches should be seen as two complementary ways of
unifying bijections between planar maps and decorated trees.Comment: 45 pages, comments welcom
The Brownian continuum random tree as the unique solution to a fixed point equation
In this note, we provide a new characterization of Aldous' Brownian continuum
random tree as the unique fixed point of a certain natural operation on
continuum trees (which gives rise to a recursive distributional equation). We
also show that this fixed point is attractive.Comment: 15 pages, 3 figure
On the algebraic numbers computable by some generalized Ehrenfest urns
This article deals with some stochastic population protocols, motivated by
theoretical aspects of distributed computing. We modelize the problem by a
large urn of black and white balls from which at every time unit a fixed number
of balls are drawn and their colors are changed according to the number of
black balls among them. When the time and the number of balls both tend to
infinity the proportion of black balls converges to an algebraic number. We
prove that, surprisingly enough, not every algebraic number can be "computed"
this way
Constellations and multicontinued fractions: application to Eulerian triangulations
We consider the problem of enumerating planar constellations with two points
at a prescribed distance. Our approach relies on a combinatorial correspondence
between this family of constellations and the simpler family of rooted
constellations, which we may formulate algebraically in terms of multicontinued
fractions and generalized Hankel determinants. As an application, we provide a
combinatorial derivation of the generating function of Eulerian triangulations
with two points at a prescribed distance.Comment: 12 pages, 4 figure
Some families of increasing planar maps
Stack-triangulations appear as natural objects when one wants to define some
increasing families of triangulations by successive additions of faces. We
investigate the asymptotic behavior of rooted stack-triangulations with
faces under two different distributions. We show that the uniform distribution
on this set of maps converges, for a topology of local convergence, to a
distribution on the set of infinite maps. In the other hand, we show that
rescaled by , they converge for the Gromov-Hausdorff topology on
metric spaces to the continuum random tree introduced by Aldous. Under a
distribution induced by a natural random construction, the distance between
random points rescaled by converge to 1 in probability.
We obtain similar asymptotic results for a family of increasing
quadrangulations
A note on the enumeration of directed animals via gas considerations
In the literature, most of the results about the enumeration of directed
animals on lattices via gas considerations are obtained by a formal passage to
the limit of enumeration of directed animals on cyclical versions of the
lattice. Here we provide a new point of view on this phenomenon. Using the gas
construction given in [Electron. J. Combin. (2007) 14 R71], we describe the gas
process on the cyclical versions of the lattices as a cyclical Markov chain
(roughly speaking, Markov chains conditioned to come back to their starting
point). Then we introduce a notion of convergence of graphs, such that if
then the gas process built on converges in distribution to
the gas process on . That gives a general tool to show that gas processes
related to animals enumeration are often Markovian on lines extracted from
lattices. We provide examples and computations of new generating functions for
directed animals with various sources on the triangular lattice, on the
lattices introduced in [Ann. Comb. 4 (2000) 269--284] and on a
generalization of the \mathcaligr {L}_n lattices introduced in [J. Phys. A 29
(1996) 3357--3365].Comment: Published in at http://dx.doi.org/10.1214/08-AAP580 the Annals of
Applied Probability (http://www.imstat.org/aap/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Random cubic planar graphs converge to the Brownian sphere
In this paper, the scaling limit of random connected cubic planar graphs
(respectively multigraphs) is shown to be the Brownian sphere.
The proof consists in essentially two main steps. First, thanks to the known
decomposition of cubic planar graphs into their 3-connected components, the
metric structure of a random cubic planar graph is shown to be well
approximated by its unique 3-connected component of linear size, with modified
distances.
Then, Whitney's theorem ensures that a 3-connected cubic planar graph is the
dual of a simple triangulation, for which it is known that the scaling limit is
the Brownian sphere. Curien and Le Gall have recently developed a framework to
study the modification of distances in general triangulations and in their
dual. By extending this framework to simple triangulations, it is shown that
3-connected cubic planar graphs with modified distances converge jointly with
their dual triangulation to the Brownian sphere.Comment: 55 page