64,591 research outputs found
Fundamental Limits of Spectral Clustering in Stochastic Block Models
We give a precise characterization of the performance of spectral clustering
for community detection under Stochastic Block Models by carrying out sharp
statistical analysis. We show spectral clustering has an exponentially small
error with matching upper and lower bounds that have the same exponent,
including the sharp leading constant. The fundamental limits established for
the spectral clustering hold for networks with multiple and imbalanced
communities and sparse networks with degrees far smaller than . The key
to our results is a novel truncated perturbation analysis for
eigenvectors and a new analysis idea of eigenvectors truncation
Clustering-based Redshift Estimation: Comparison to Spectroscopic Redshifts
We investigate the potential and accuracy of clustering-based redshift
estimation using the method proposed by M\'enard et al. (2013). This technique
enables the inference of redshift distributions from measurements of the
spatial clustering of arbitrary sources, using a set of reference objects for
which redshifts are known. We apply it to a sample of spectroscopic galaxies
from the Sloan Digital Sky Survey and show that, after carefully controlling
the sampling efficiency over the sky, we can estimate redshift distributions
with high accuracy. Probing the full colour space of the SDSS galaxies, we show
that we can recover the corresponding mean redshifts with an accuracy ranging
from z=0.001 to 0.01. We indicate that this mapping can be used to
infer the redshift probability distribution of a single galaxy. We show how the
lack of information on the galaxy bias limits the accuracy of the inference and
show comparisons between clustering redshifts and photometric redshifts for
this dataset. This analysis demonstrates, using real data, that
clustering-based redshift inference provides a powerful data-driven technique
to explore the redshift distribution of arbitrary datasets, without any prior
knowledge on the spectral energy distribution of the sources.Comment: 13 pages. Submitted to MNRAS. Comments welcom
Community detection and stochastic block models: recent developments
The stochastic block model (SBM) is a random graph model with planted
clusters. It is widely employed as a canonical model to study clustering and
community detection, and provides generally a fertile ground to study the
statistical and computational tradeoffs that arise in network and data
sciences.
This note surveys the recent developments that establish the fundamental
limits for community detection in the SBM, both with respect to
information-theoretic and computational thresholds, and for various recovery
requirements such as exact, partial and weak recovery (a.k.a., detection). The
main results discussed are the phase transitions for exact recovery at the
Chernoff-Hellinger threshold, the phase transition for weak recovery at the
Kesten-Stigum threshold, the optimal distortion-SNR tradeoff for partial
recovery, the learning of the SBM parameters and the gap between
information-theoretic and computational thresholds.
The note also covers some of the algorithms developed in the quest of
achieving the limits, in particular two-round algorithms via graph-splitting,
semi-definite programming, linearized belief propagation, classical and
nonbacktracking spectral methods. A few open problems are also discussed
Detection of the Cosmic Far-Infrared Background in the AKARI Deep Field South
We report the detection and measurement of the absolute brightness and
spatial fluctuations of the cosmic infrared background (CIB) with the AKARI
satellite. We have carried out observations at 65, 90, 140 and 160 um as a
cosmological survey in AKARI Deep Field South (ADF-S), which is one of the
lowest cirrus regions with contiguous area on the sky. After removing bright
galaxies and subtracting zodiacal and Galactic foregrounds from the measured
sky brightness, we have successfully measured the CIB brightness and its
fluctuations across a wide range of angular scales from arcminutes to degrees.
The measured CIB brightness is consistent with previous results reported from
COBE data but significantly higher than the lower limits at 70 and 160 um
obtained with the Spitzer satellite from the stacking analysis of 24-um
selected sources. The discrepancy with the Spitzer result is possibly due to a
new galaxy population at high redshift obscured by hot dust. From power
spectrum analysis at 90 um, three components are identified: shot noise due to
individual galaxies; Galactic cirrus emission dominating at the largest angular
scales of a few degrees; and an additional component at an intermediate angular
scale of 10-30 arcminutes, possibly due to galaxy clustering. The spectral
shape of the clustering component at 90 um is very similar to that at longer
wavelengths as observed by Spitzer and BLAST. Moreover, the color of the
fluctuations indicates that the clustering component is as red as
Ultra-luminous infrared galaxies (ULIRGs) at high redshift, These galaxies are
not likely to be the majority of the CIB emission at 90 um, but responsible for
the clustering component. Our results provide new constraints on the evolution
and clustering properties of distant infrared galaxies.Comment: 50 pages, 15 figures, submitted to Ap
Fluctuation Operators and Spontaneous Symmetry Breaking
We develop an alternative approach to this field, which was to a large extent
developed by Verbeure et al. It is meant to complement their approach, which is
largely based on a non-commutative central limit theorem and coordinate space
estimates. In contrast to that we deal directly with the limits of -point
truncated correlation functions and show that they typically vanish for provided that the respective scaling exponents of the fluctuation
observables are appropriately chosen. This direct approach is greatly
simplified by the introduction of a smooth version of spatial averaging, which
has a much nicer scaling behavior and the systematic developement of Fourier
space and energy-momentum spectral methods. We both analyze the regime of
normal fluctuations, the various regimes of poor clustering and the case of
spontaneous symmetry breaking or Goldstone phenomenon.Comment: 30 pages, Latex, a more detailed discussion in section 7 as to
possible scaling behavior of l-point function
Spectral Efficient and Energy Aware Clustering in Cellular Networks
The current and envisaged increase of cellular traffic poses new challenges
to Mobile Network Operators (MNO), who must densify their Radio Access Networks
(RAN) while maintaining low Capital Expenditure and Operational Expenditure to
ensure long-term sustainability. In this context, this paper analyses optimal
clustering solutions based on Device-to-Device (D2D) communications to mitigate
partially or completely the need for MNOs to carry out extremely dense RAN
deployments. Specifically, a low complexity algorithm that enables the creation
of spectral efficient clusters among users from different cells, denoted as
enhanced Clustering Optimization for Resources' Efficiency (eCORE) is
presented. Due to the imbalance between uplink and downlink traffic, a
complementary algorithm, known as Clustering algorithm for Load Balancing
(CaLB), is also proposed to create non-spectral efficient clusters when they
result in a capacity increase. Finally, in order to alleviate the energy
overconsumption suffered by cluster heads, the Clustering Energy Efficient
algorithm (CEEa) is also designed to manage the trade-off between the capacity
enhancement and the early battery drain of some users. Results show that the
proposed algorithms increase the network capacity and outperform existing
solutions, while, at the same time, CEEa is able to handle the cluster heads
energy overconsumption
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