4,293 research outputs found
A Neural Networks Committee for the Contextual Bandit Problem
This paper presents a new contextual bandit algorithm, NeuralBandit, which
does not need hypothesis on stationarity of contexts and rewards. Several
neural networks are trained to modelize the value of rewards knowing the
context. Two variants, based on multi-experts approach, are proposed to choose
online the parameters of multi-layer perceptrons. The proposed algorithms are
successfully tested on a large dataset with and without stationarity of
rewards.Comment: 21st International Conference on Neural Information Processin
On the accuracy of the ALI method for solving the radiative transfer equation
We solve the integral equation describing the propagation of light in an
isothermal plane-parallel atmosphere of optical thickness , adopting a
uniform thermalization parameter . The solution given by the ALI
method, widely used in the field of stellar atmospheres modelling, is compared
to the exact solution. Graphs are given that illustrate the accuracy of the ALI
solution as a function of the parameters , and optical depth
variable .Comment: 7 pages, 11 figures, A&A, accepted 30 July 2003, minor correction
Preconditioned Bi-Conjugate Gradient Method for Radiative Transfer in Spherical Media
A robust numerical method called the Preconditioned Bi-Conjugate Gradient
(Pre-BiCG)method is proposed for the solution of radiative transfer equation in
spherical geometry.A variant of this method called Stabilized Preconditioned
Bi-Conjugate Gradient (Pre-BiCG-STAB) is also presented. These are iterative
methods based on the construction of a set of bi-orthogonal vectors. The
application of Pre-BiCG method in some benchmark tests show that the method is
quite versatile, and can handle hard problems that may arise in astrophysical
radiative transfer theory.Comment: 19 pages, 12 figure
Spinodal fractionation in a polydisperse square well fluid
Using Kinetic Monte Carlo simulation, we model gas-liquid spinodal
decomposition in a size-polydisperse square well fluid, representing a
'near-monodisperse' colloidal dispersion. We find that fractionation (demixing)
of particle sizes between the phases begins asserting itself shortly after the
onset of phase ordering. Strikingly, the direction of size fractionation can be
reversed by a seemingly trivial choice between two inter-particle potentials
which, in the monodisperse case, are identical -- we rationalise this in terms
of a perturbative, equilibrium theory of polydispersity. Furthermore, our
quantitative results show that Kinetic Monte Carlo simulation can provide
detailed insight into the role of fractionation in real colloidal systems.Comment: 7 pages, 7 figures, to be published in Phys. Rev.
Concurrent bandits and cognitive radio networks
We consider the problem of multiple users targeting the arms of a single
multi-armed stochastic bandit. The motivation for this problem comes from
cognitive radio networks, where selfish users need to coexist without any side
communication between them, implicit cooperation or common control. Even the
number of users may be unknown and can vary as users join or leave the network.
We propose an algorithm that combines an -greedy learning rule with a
collision avoidance mechanism. We analyze its regret with respect to the
system-wide optimum and show that sub-linear regret can be obtained in this
setting. Experiments show dramatic improvement compared to other algorithms for
this setting
Bootstrapping Monte Carlo Tree Search with an Imperfect Heuristic
We consider the problem of using a heuristic policy to improve the value
approximation by the Upper Confidence Bound applied in Trees (UCT) algorithm in
non-adversarial settings such as planning with large-state space Markov
Decision Processes. Current improvements to UCT focus on either changing the
action selection formula at the internal nodes or the rollout policy at the
leaf nodes of the search tree. In this work, we propose to add an auxiliary arm
to each of the internal nodes, and always use the heuristic policy to roll out
simulations at the auxiliary arms. The method aims to get fast convergence to
optimal values at states where the heuristic policy is optimal, while retaining
similar approximation as the original UCT in other states. We show that
bootstrapping with the proposed method in the new algorithm, UCT-Aux, performs
better compared to the original UCT algorithm and its variants in two benchmark
experiment settings. We also examine conditions under which UCT-Aux works well.Comment: 16 pages, accepted for presentation at ECML'1
Oblivion: Mitigating Privacy Leaks by Controlling the Discoverability of Online Information
Search engines are the prevalently used tools to collect information about
individuals on the Internet. Search results typically comprise a variety of
sources that contain personal information -- either intentionally released by
the person herself, or unintentionally leaked or published by third parties,
often with detrimental effects on the individual's privacy. To grant
individuals the ability to regain control over their disseminated personal
information, the European Court of Justice recently ruled that EU citizens have
a right to be forgotten in the sense that indexing systems, must offer them
technical means to request removal of links from search results that point to
sources violating their data protection rights. As of now, these technical
means consist of a web form that requires a user to manually identify all
relevant links upfront and to insert them into the web form, followed by a
manual evaluation by employees of the indexing system to assess if the request
is eligible and lawful.
We propose a universal framework Oblivion to support the automation of the
right to be forgotten in a scalable, provable and privacy-preserving manner.
First, Oblivion enables a user to automatically find and tag her disseminated
personal information using natural language processing and image recognition
techniques and file a request in a privacy-preserving manner. Second, Oblivion
provides indexing systems with an automated and provable eligibility mechanism,
asserting that the author of a request is indeed affected by an online
resource. The automated ligibility proof ensures censorship-resistance so that
only legitimately affected individuals can request the removal of corresponding
links from search results. We have conducted comprehensive evaluations, showing
that Oblivion is capable of handling 278 removal requests per second, and is
hence suitable for large-scale deployment
Synthetic spectra of H Balmer and HeI absorption lines. I: Stellar library
We present a grid of synthetic profiles of stellar H Balmer and HeI lines at
optical wavelengths with a sampling of 0.3 A. The grid spans a range of
effective temperature 4000 K < Teff < 50000 K, and gravity 0.0 < log g < 5.0 at
solar metallicity. For Teff > 25000 K, NLTE stellar atmosphere models are
computed using the code TLUSTY (Hubeny 1988). For cooler stars, Kurucz (1993)
LTE models are used to compute thesynthetic spectra. The grid includes the
profiles of the high-order hydrogen Balmer series and HeI lines for effective
temperatures and gravities that have not been previously synthesized. The
behavior of H8 to H13 and HeI 3819 with effective temperature and gravity is
very similar to that of the lower terms of the series (e.g. Hb) and the other
HeI lines at longer wavelengths; therefore, they are suited for the
determination of the atmospheric parameters of stars. These lines are
potentially important to make predictions for these stellar absorption features
in galaxies with active star formation. Evolutionary synthesis models of these
lines for starburst and post-starburst galaxies are presented in a companion
paper. The full set of the synthetic stellar spectra is available for retrieval
at our website http://www.iaa.es/ae/e2.html and
http://www.stsci.edu/science/starburst/ or on request from the authors at
[email protected]: To be published in ApJS. 28 pages and 12 figure
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