500 research outputs found
Percolation on dense graph sequences
In this paper we determine the percolation threshold for an arbitrary
sequence of dense graphs . Let be the largest eigenvalue of
the adjacency matrix of , and let be the random subgraph of
obtained by keeping each edge independently with probability . We
show that the appearance of a giant component in has a sharp
threshold at . In fact, we prove much more: if
converges to an irreducible limit, then the density of the largest component of
tends to the survival probability of a multi-type branching process
defined in terms of this limit. Here the notions of convergence and limit are
those of Borgs, Chayes, Lov\'asz, S\'os and Vesztergombi. In addition to using
basic properties of convergence, we make heavy use of the methods of
Bollob\'as, Janson and Riordan, who used multi-type branching processes to
study the emergence of a giant component in a very broad family of sparse
inhomogeneous random graphs.Comment: Published in at http://dx.doi.org/10.1214/09-AOP478 the Annals of
Probability (http://www.imstat.org/aop/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Limits of dense graph sequences
We show that if a sequence of dense graphs has the property that for every
fixed graph F, the density of copies of F in these graphs tends to a limit,
then there is a natural ``limit object'', namely a symmetric measurable
2-variable function on [0,1]. This limit object determines all the limits of
subgraph densities. We also show that the graph parameters obtained as limits
of subgraph densities can be characterized by ``reflection positivity'',
semidefiniteness of an associated matrix. Conversely, every such function
arises as a limit object. Along the lines we introduce a rather general model
of random graphs, which seems to be interesting on its own right.Comment: 27 pages; added extension of result (Sept 22, 2004
-limit of the cut functional on dense graph sequences
A sequence of graphs with diverging number of nodes is a dense graph sequence
if the number of edges grows approximately as for complete graphs. To each such
sequence a function, called graphon, can be associated, which contains
information about the asymptotic behavior of the sequence. Here we show that
the problem of subdividing a large graph in communities with a minimal amount
of cuts can be approached in terms of graphons and the -limit of the
cut functional, and discuss the resulting variational principles on some
examples. Since the limit cut functional is naturally defined on Young
measures, in many instances the partition problem can be expressed in terms of
the probability that a node belongs to one of the communities. Our approach can
be used to obtain insights into the bisection problem for large graphs, which
is known to be NP-complete.Comment: 25 pages, 5 figure
Chromatic roots and limits of dense graphs
In this short note we observe that recent results of Abert and Hubai and of
Csikvari and Frenkel about Benjamini--Schramm continuity of the holomorphic
moments of the roots of the chromatic polynomial extend to the theory of dense
graph sequences. We offer a number of problems and conjectures motivated by
this observation.Comment: 9 page
Glauber Dynamics for Ising Model on Convergent Dense Graph Sequences
We study the Glauber dynamics for Ising model on (sequences of) dense graphs. We view the dense graphs through the lens of graphons. For the ferromagnetic Ising model with inverse temperature beta on a convergent sequence of graphs G_n with limit graphon W we show fast mixing of the Glauber dynamics if beta * lambda_1(W) 1 (where lambda_1(W)is the largest eigenvalue of the graphon). We also show that in the case beta * lambda_1(W) = 1 there is insufficient information to determine the mixing time (it can be either fast or slow)
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