22 research outputs found
Local cluster aggregation models of explosive percolation
We introduce perhaps the simplest models of graph evolution with choice that
demonstrate discontinuous percolation transitions and can be analyzed via
mathematical evolution equations. These models are local, in the sense that at
each step of the process one edge is selected from a small set of potential
edges sharing common vertices and added to the graph. We show that the
evolution can be accurately described by a system of differential equations and
that such models exhibit the discontinuous emergence of the giant component.
Yet, they also obey scaling behaviors characteristic of continuous transitions,
with scaling exponents that differ from the classic Erdos-Renyi model.Comment: Final version as appearing in PR
Strongly discontinuous explosive percolation with multiple giant components
We generalize the random graph evolution process of Bohman, Frieze, and
Wormald [T. Bohman, A. Frieze, and N. C. Wormald, Random Struct. Algorithms,
25, 432 (2004)]. Potential edges, sampled uniformly at random from the complete
graph, are considered one at a time and either added to the graph or rejected
provided that the fraction of accepted edges is never smaller than a decreasing
function asymptotically approaching the value alpha = 1/2. We show that
multiple giant components appear simultaneously in a strongly discontinuous
percolation transition and remain distinct. Furthermore, tuning the value of
alpha determines the number of such components with smaller alpha leading to an
increasingly delayed and more explosive transition. The location of the
critical point and strongly discontinuous nature are not affected if only edges
which span components are sampled.Comment: Final version appearing in PR
Network Growth with Feedback
Existing models of network growth typically have one or two parameters or
strategies which are fixed for all times. We introduce a general framework
where feedback on the current state of a network is used to dynamically alter
the values of such parameters. A specific model is analyzed where limited
resources are shared amongst arriving nodes, all vying to connect close to the
root. We show that tunable feedback leads to growth of larger, more efficient
networks. Exact results show that linear scaling of resources with system size
yields crossover to a trivial condensed state, which can be considerably
delayed with sublinear scaling.Comment: 4 pages, 4 figure
Resilience and rewiring of the passenger airline networks in the United States
The air transportation network, a fundamental component of critical
infrastructure, is formed from a collection of individual air carriers, each
one with a methodically designed and engineered network structure. We analyze
the individual structures of the seven largest passenger carriers in the USA
and find that networks with dense interconnectivity, as quantified by large
k-cores for high values of k, are extremely resilient to both targeted removal
of airports (nodes) and random removal of flight paths paths (edges). Such
networks stay connected and incur minimal increase in an heuristic travel time
despite removal of a majority of nodes or edges. Similar results are obtained
for targeted removal based on either node degree or centrality. We introduce
network rewiring schemes that boost resilience to different levels of
perturbation while preserving total number of flight and gate requirements.
Recent studies have focused on the asymptotic optimality of hub-and-spoke
spatial networks under normal operating conditions, yet our results indicate
that point-to-point architectures can be much more resilient to perturbations.Comment: 11 pages, 8 figures, replaced by the version to appear in Physical
Review
BML revisited: Statistical physics, computer simulation and probability
Statistical physics, computer simulation and discrete mathematics are intimately related through the study of shared lattice models. These models lie at the foundation of all three fields, are studied extensively, and can be highly influential. Yet new computational and mathematical tools may challenge even well established beliefs. Consider the BML model, which is a paradigm for modeling self-organized patterns of traffic flow and first-order jamming transitions. Recent findings, on the existence of intermediate states, bring into question the standard understanding of the jamming transition. We review the results and show that the onset of full-jamming can be considerably delayed based on the geometry of the system. We also introduce an asynchronous version of BML, which lacks the self-organizing properties of BML, has none of the puzzling intermediate states, but has a sharp, discontinuous, transition to full jamming. We believe this asynchronous version will be more amenable to rigorous mathematical analysis than standard BML. We discuss additional models, such as bootstrap percolation, the honey-comb dimer model and the rotor-router, all of which exemplify the interplay between the three fields, while also providing cautionary tales. Finally, we synthesize implications for how results from one field may relate to the other, and also implications specific to computer implementations.