8,408 research outputs found
Narrow scope for resolution-limit-free community detection
Detecting communities in large networks has drawn much attention over the
years. While modularity remains one of the more popular methods of community
detection, the so-called resolution limit remains a significant drawback. To
overcome this issue, it was recently suggested that instead of comparing the
network to a random null model, as is done in modularity, it should be compared
to a constant factor. However, it is unclear what is meant exactly by
"resolution-limit-free", that is, not suffering from the resolution limit.
Furthermore, the question remains what other methods could be classified as
resolution-limit-free. In this paper we suggest a rigorous definition and
derive some basic properties of resolution-limit-free methods. More
importantly, we are able to prove exactly which class of community detection
methods are resolution-limit-free. Furthermore, we analyze which methods are
not resolution-limit-free, suggesting there is only a limited scope for
resolution-limit-free community detection methods. Finally, we provide such a
natural formulation, and show it performs superbly
Analysis of group evolution prediction in complex networks
In the world, in which acceptance and the identification with social
communities are highly desired, the ability to predict evolution of groups over
time appears to be a vital but very complex research problem. Therefore, we
propose a new, adaptable, generic and mutli-stage method for Group Evolution
Prediction (GEP) in complex networks, that facilitates reasoning about the
future states of the recently discovered groups. The precise GEP modularity
enabled us to carry out extensive and versatile empirical studies on many
real-world complex / social networks to analyze the impact of numerous setups
and parameters like time window type and size, group detection method,
evolution chain length, prediction models, etc. Additionally, many new
predictive features reflecting the group state at a given time have been
identified and tested. Some other research problems like enriching learning
evolution chains with external data have been analyzed as well
Baryon oscillations in galaxy and matter power-spectrum covariance matrices
We investigate large-amplitude baryon acoustic oscillations (BAO's) in
off-diagonal entries of cosmological power-spectrum covariance matrices. These
covariance-matrix BAO's describe the increased attenuation of power-spectrum
BAO's caused by upward fluctuations in large-scale power. We derive an analytic
approximation to covariance-matrix entries in the BAO regime, and check the
analytical predictions using N-body simulations. These BAO's look much stronger
than the BAO's in the power spectrum, but seem detectable only at about a
one-sigma level in gigaparsec-scale galaxy surveys. In estimating cosmological
parameters using matter or galaxy power spectra, including the
covariance-matrix BAO's can have a several-percent effect on error-bar widths
for some parameters directly related to the BAO's, such as the baryon fraction.
Also, we find that including the numerous galaxies in small haloes in a survey
can reduce error bars in these cosmological parameters more than the simple
reduction in shot noise might suggest.Comment: 11 pages, 11 figures, accepted to MNRAS. Minor changes to match
accepted version. CosmoPy (Cosmological Python) code available at
http://ifa.hawaii.edu/cosmopy
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