2,166 research outputs found
On the Convergence of Alternating Direction Lagrangian Methods for Nonconvex Structured Optimization Problems
Nonconvex and structured optimization problems arise in many engineering
applications that demand scalable and distributed solution methods. The study
of the convergence properties of these methods is in general difficult due to
the nonconvexity of the problem. In this paper, two distributed solution
methods that combine the fast convergence properties of augmented
Lagrangian-based methods with the separability properties of alternating
optimization are investigated. The first method is adapted from the classic
quadratic penalty function method and is called the Alternating Direction
Penalty Method (ADPM). Unlike the original quadratic penalty function method,
in which single-step optimizations are adopted, ADPM uses an alternating
optimization, which in turn makes it scalable. The second method is the
well-known Alternating Direction Method of Multipliers (ADMM). It is shown that
ADPM for nonconvex problems asymptotically converges to a primal feasible point
under mild conditions and an additional condition ensuring that it
asymptotically reaches the standard first order necessary conditions for local
optimality are introduced. In the case of the ADMM, novel sufficient conditions
under which the algorithm asymptotically reaches the standard first order
necessary conditions are established. Based on this, complete convergence of
ADMM for a class of low dimensional problems are characterized. Finally, the
results are illustrated by applying ADPM and ADMM to a nonconvex localization
problem in wireless sensor networks.Comment: 13 pages, 6 figure
Theories for influencer identification in complex networks
In social and biological systems, the structural heterogeneity of interaction
networks gives rise to the emergence of a small set of influential nodes, or
influencers, in a series of dynamical processes. Although much smaller than the
entire network, these influencers were observed to be able to shape the
collective dynamics of large populations in different contexts. As such, the
successful identification of influencers should have profound implications in
various real-world spreading dynamics such as viral marketing, epidemic
outbreaks and cascading failure. In this chapter, we first summarize the
centrality-based approach in finding single influencers in complex networks,
and then discuss the more complicated problem of locating multiple influencers
from a collective point of view. Progress rooted in collective influence
theory, belief-propagation and computer science will be presented. Finally, we
present some applications of influencer identification in diverse real-world
systems, including online social platforms, scientific publication, brain
networks and socioeconomic systems.Comment: 24 pages, 6 figure
Multitask Diffusion Adaptation over Networks
Adaptive networks are suitable for decentralized inference tasks, e.g., to
monitor complex natural phenomena. Recent research works have intensively
studied distributed optimization problems in the case where the nodes have to
estimate a single optimum parameter vector collaboratively. However, there are
many important applications that are multitask-oriented in the sense that there
are multiple optimum parameter vectors to be inferred simultaneously, in a
collaborative manner, over the area covered by the network. In this paper, we
employ diffusion strategies to develop distributed algorithms that address
multitask problems by minimizing an appropriate mean-square error criterion
with -regularization. The stability and convergence of the algorithm in
the mean and in the mean-square sense is analyzed. Simulations are conducted to
verify the theoretical findings, and to illustrate how the distributed strategy
can be used in several useful applications related to spectral sensing, target
localization, and hyperspectral data unmixing.Comment: 29 pages, 11 figures, submitted for publicatio
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