154,380 research outputs found
Ordered community structure in networks
Community structure in networks is often a consequence of homophily, or
assortative mixing, based on some attribute of the vertices. For example,
researchers may be grouped into communities corresponding to their research
topic. This is possible if vertex attributes have discrete values, but many
networks exhibit assortative mixing by some continuous-valued attribute, such
as age or geographical location. In such cases, no discrete communities can be
identified. We consider how the notion of community structure can be
generalized to networks that are based on continuous-valued attributes: in
general, a network may contain discrete communities which are ordered according
to their attribute values. We propose a method of generating synthetic ordered
networks and investigate the effect of ordered community structure on the
spread of infectious diseases. We also show that community detection algorithms
fail to recover community structure in ordered networks, and evaluate an
alternative method using a layout algorithm to recover the ordering.Comment: This is an extended preprint version that includes an extra example:
the college football network as an ordered (spatial) network. Further
improvements, not included here, appear in the journal version. Original
title changed (from "Ordered and continuous community structure in networks")
to match journal versio
Analysis and Assembling of Network Structure in Mutualistic Systems
It has been observed that mutualistic bipartite networks have a nested
structure of interactions. In addition, the degree distributions associated
with the two guilds involved in such networks (e.g. plants & pollinators or
plants & seed dispersers) approximately follow a truncated power law. We show
that nestedness and truncated power law distributions are intimately linked,
and that any biological reasons for such truncation are superimposed to finite
size effects . We further explore the internal organization of bipartite
networks by developing a self-organizing network model (SNM) that reproduces
empirical observations of pollination systems of widely different sizes. Since
the only inputs to the SNM are numbers of plant and animal species, and their
interactions (i.e., no data on local abundance of the interacting species are
needed), we suggest that the well-known association between species frequency
of interaction and species degree is a consequence rather than a cause, of the
observed network structure.Comment: J. of. Theor. Biology, in pres
Community Structure in Time-Dependent, Multiscale, and Multiplex Networks
Network science is an interdisciplinary endeavor, with methods and
applications drawn from across the natural, social, and information sciences. A
prominent problem in network science is the algorithmic detection of
tightly-connected groups of nodes known as communities. We developed a
generalized framework of network quality functions that allowed us to study the
community structure of arbitrary multislice networks, which are combinations of
individual networks coupled through links that connect each node in one network
slice to itself in other slices. This framework allows one to study community
structure in a very general setting encompassing networks that evolve over
time, have multiple types of links (multiplexity), and have multiple scales.Comment: 31 pages, 3 figures, 1 table. Includes main text and supporting
material. This is the accepted version of the manuscript (the definitive
version appeared in Science), with typographical corrections included her
The co-evolution of emotional well-being with weak and strong friendship ties
Social ties are strongly related to well-being. But what characterizes this
relationship? This study investigates social mechanisms explaining how social
ties affect well-being through social integration and social influence, and how
well-being affects social ties through social selection. We hypothesize that
highly integrated individuals - those with more extensive and dense friendship
networks - report higher emotional well-being than others. Moreover, emotional
well-being should be influenced by the well-being of close friends. Finally,
well-being should affect friendship selection when individuals prefer others
with higher levels of well-being, and others whose well-being is similar to
theirs. We test our hypotheses using longitudinal social network and well-being
data of 117 individuals living in a graduate housing community. The application
of a novel extension of Stochastic Actor-Oriented Models for ordered networks
(ordered SAOMs) allows us to detail and test our hypotheses for weak- and
strong-tied friendship networks simultaneously. Results do not support our
social integration and social influence hypotheses but provide evidence for
selection: individuals with higher emotional well-being tend to have more
strong-tied friends, and there are homophily processes regarding emotional
well-being in strong-tied networks. Our study highlights the two-directional
relationship between social ties and well-being, and demonstrates the
importance of considering different tie strengths for various social processes
Searching for network modules
When analyzing complex networks a key target is to uncover their modular
structure, which means searching for a family of modules, namely node subsets
spanning each a subnetwork more densely connected than the average. This work
proposes a novel type of objective function for graph clustering, in the form
of a multilinear polynomial whose coefficients are determined by network
topology. It may be thought of as a potential function, to be maximized, taking
its values on fuzzy clusterings or families of fuzzy subsets of nodes over
which every node distributes a unit membership. When suitably parametrized,
this potential is shown to attain its maximum when every node concentrates its
all unit membership on some module. The output thus is a partition, while the
original discrete optimization problem is turned into a continuous version
allowing to conceive alternative search strategies. The instance of the problem
being a pseudo-Boolean function assigning real-valued cluster scores to node
subsets, modularity maximization is employed to exemplify a so-called quadratic
form, in that the scores of singletons and pairs also fully determine the
scores of larger clusters, while the resulting multilinear polynomial potential
function has degree 2. After considering further quadratic instances, different
from modularity and obtained by interpreting network topology in alternative
manners, a greedy local-search strategy for the continuous framework is
analytically compared with an existing greedy agglomerative procedure for the
discrete case. Overlapping is finally discussed in terms of multiple runs, i.e.
several local searches with different initializations.Comment: 10 page
Community detection with spiking neural networks for neuromorphic hardware
We present results related to the performance of an algorithm for community
detection which incorporates event-driven computation. We define a mapping
which takes a graph G to a system of spiking neurons. Using a fully connected
spiking neuron system, with both inhibitory and excitatory synaptic
connections, the firing patterns of neurons within the same community can be
distinguished from firing patterns of neurons in different communities. On a
random graph with 128 vertices and known community structure we show that by
using binary decoding and a Hamming-distance based metric, individual
communities can be identified from spike train similarities. Using bipolar
decoding and finite rate thresholding, we verify that inhibitory connections
prevent the spread of spiking patterns.Comment: Conference paper presented at ORNL Neuromorphic Workshop 2017, 7
pages, 6 figure
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