1,241 research outputs found
How to calculate the barycenter of a weighted graph
Discrete structures like graphs make it possible to naturally and exibly model complex phenomena. Since graphs that represent various types of information are increasingly available today, their analysis has become a popular subject of research. The graphs studied in the field of data science at this time generally have a large number of nodes that are not fairly weighted and connected to each other, translating a structural specification of the data. Yet, even an algorithm for locating the average position in graphs is lacking although this knowledge would be of primary interest for statistical or representation problems. In this work, we develop a stochastic algorithm for finding the Fréchet mean of weighted undirected metric graphs. This method relies on a noisy simulated annealing algorithm dealt with using homogenization. We then illustrate our algorithm with two examples (subgraphs of a social network and of a collaboration and citation network)
How to calculate the barycenter of a weighted graph
Discrete structures like graphs make it possible to naturally and exibly model complex phenomena. Since graphs that represent various types of information are increasingly available today, their analysis has become a popular subject of research. The graphs studied in the field of data science at this time generally have a large number of nodes that are not fairly weighted and connected to each other, translating a structural specification of the data. Yet, even an algorithm for locating the average position in graphs is lacking although this knowledge would be of primary interest for statistical or representation problems. In this work, we develop a stochastic algorithm for finding the Fréchet mean of weighted undirected metric graphs. This method relies on a noisy simulated annealing algorithm dealt with using homogenization. We then illustrate our algorithm with two examples (subgraphs of a social network and of a collaboration and citation network)
Convex Hull Realizations of the Multiplihedra
We present a simple algorithm for determining the extremal points in
Euclidean space whose convex hull is the nth polytope in the sequence known as
the multiplihedra. This answers the open question of whether the multiplihedra
could be realized as convex polytopes. We use this realization to unite the
approach to A_n-maps of Iwase and Mimura to that of Boardman and Vogt. We
include a review of the appearance of the nth multiplihedron for various n in
the studies of higher homotopy commutativity, (weak) n-categories,
A_infinity-categories, deformation theory, and moduli spaces. We also include
suggestions for the use of our realizations in some of these areas as well as
in related studies, including enriched category theory and the graph
associahedra.Comment: typos fixed, introduction revise
Evolution of circumbinary planets around eccentric binaries: The case of Kepler-34
The existence of planets orbiting a central binary star system immediately
raises questions regarding their formation and dynamical evolution. Recent
discoveries of circumbinary planets by the Kepler space telescope has shown
that some of these planets reside close to the dynamical stability limit where
it is very difficult to form planets in situ. For binary systems with nearly
circular orbits, such as Kepler-38, the observed proximity of planetary orbits
to the stability limit can be understood by an evolutionary process in which
planets form farther out in the disk and migrate inward to their observed
position. The Kepler-34 system has a high orbital eccentricity of 0.52. Here,
we analyse evolutionary scenarios for the planet observed around this system
using two-dimensional hydrodynamical simulations.
The highly eccentric binary opens a wide inner hole in the disk which is also
eccentric, and displays a slow prograde precession. As a result of the large,
eccentric inner gap, an embedded planet settles in a final equilibrium position
that lies beyond the observed location of Kepler-34 b, but has the correct
eccentricity. In this configuration the planetary orbit is aligned with the
disk in a state of apsidal corotation.To account for the closer orbit of
Kepler-34 b to the central binary, we considered a two-planet scenario and
examined the evolution of the system through joint inward migration and capture
into mean-motion resonances. When the inner planet orbits inside the gap of the
disk, planet-planet scattering ensues. While often one object is thrown into a
large, highly eccentric orbit, at times the system is left with a planet close
to the observed orbit, suggesting that Kepler 34 might have had two
circumbinary planets where one might have been scattered out of the system or
into an orbit where it did not transit the central binary during the operation
of Kepler.Comment: 11 pages, 13 figures, accepted by Astronomy & Astrophysics. arXiv
admin note: text overlap with arXiv:1401.764
Towards Swarm Calculus: Urn Models of Collective Decisions and Universal Properties of Swarm Performance
Methods of general applicability are searched for in swarm intelligence with
the aim of gaining new insights about natural swarms and to develop design
methodologies for artificial swarms. An ideal solution could be a `swarm
calculus' that allows to calculate key features of swarms such as expected
swarm performance and robustness based on only a few parameters. To work
towards this ideal, one needs to find methods and models with high degrees of
generality. In this paper, we report two models that might be examples of
exceptional generality. First, an abstract model is presented that describes
swarm performance depending on swarm density based on the dichotomy between
cooperation and interference. Typical swarm experiments are given as examples
to show how the model fits to several different results. Second, we give an
abstract model of collective decision making that is inspired by urn models.
The effects of positive feedback probability, that is increasing over time in a
decision making system, are understood by the help of a parameter that controls
the feedback based on the swarm's current consensus. Several applicable
methods, such as the description as Markov process, calculation of splitting
probabilities, mean first passage times, and measurements of positive feedback,
are discussed and applications to artificial and natural swarms are reported
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