8710 articles  [version française]
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Publications HAL de la collection INRIA-RRRT

2014

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Titre
Accurate computation of single scattering in participating media with refractive boundaries
Auteurs
Nicolas Holzschuch url
Détail
[Research Report], 2014, pp. 22. RR-8312
Début du résumé
Volume caustics are high-frequency effects appearing in participating media with low opacity, when refractive interfaces are focusing the light rays. Refractions make them hard to compute, since screen locality does not correlate with spatial locality in the medium. In this paper we give a new method for accurate computation of single scattering effects in a participating media enclosed by refractive interfaces. Our algorithm is based on the observation that although radiance along each camera ray is irregular, contributions from individual triangles are smooth. Our method gives more accurate results than existing methods, faster. It uses minimal information and requires no .....
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squelette-rr.pdf BibTex
Titre
Towards a Generic API for Data Load Balancing in Structured P2P Systems
Auteurs
Maeva Antoine; Laurent Pellegrino url; Fabrice Huet; Françoise Baude
Détail
[Research Report], 2014, pp. 18. RR-8564
Début du résumé
Many structured Peer-to-Peer systems for data management face the problem of load imbalance. To address this issue, there exist almost as many load balancing strategies as there are different systems. Besides, the proposed solutions are often coupled to their own API, making it difficult to port a scheme from a system to another. In this report, we show that many load balancing schemes are comprised of the same basic elements, and only the implementation and interconnection of these elements vary. Based on this observation, we describe the concepts behind the building of a common API to implement any load balancing .....
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Titre
Mapped Fourier Methods for stiff problems in toroidal geometry
Auteurs
Herve Guillard
Détail
[Research Report], 2014, pp. 17. RR-8566
Début du résumé
Fourier spectral or pseudo-spectral methods are usually extremely efficient for periodic problems. However this efficiency is lost if the solutions have zones of rapid variations or internal layers. For these cases, a large number of Fourier modes are required and this makes the Fourier method unpractical in many cases. This work investigates the use of mapped Fourier method as a way to circumvent this problem. Mapped Fourier method uses instead of the usual Fourier interpolant the composition of the Fourier interpolant with a mapping in such a way that in the computational space, the functions to represent are not stiff. .....
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Titre
Bandits Warm-up Cold Recommender Systems
Auteurs
Jérémie Mary; Romaric Gaudel; Preux Philippe url
Détail
[Research Report], 2014, pp. 18. RR-8563
Début du résumé
We address the cold start problem in recommendation systems assuming no contextual information is available neither about users, nor items. We consider the case in which we only have access to a set of ratings of items by users. Most of the existing works consider a batch setting, and use cross-validation to tune parameters. The classical method consists in minimizing the root mean square error over a training subset of the ratings which provides a factorization of the matrix of ratings, interpreted as a latent representation of items and users. Our contribution in this paper is 5-fold. First, we explicit .....
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Titre
Comparison of numerical solvers for anisotropic diffusion equations arising in plasma physics
Auteurs
Nicolas Crouseilles url; Matthieu Kuhn; Guillaume Latu
Détail
[Research Report], 2014. RR-8560
Début du résumé
This work is devoted to the comparison of numerical schemes to approximate anisotropic diffusion problems arising in tokamak plasma physics. We focus on the spatial approximation by using finite volume method and on the time discretization. This latter point is delicate since the use of explicit integrators leads to a severe restriction on the time step. Then, implicit and semi-implicit schemes are coupled to finite volumes space discretization and are compared for some classical problems relevant for magnetically confined plasmas. It appears that the semi-implicit approaches (using ARK methods or directional splitting) turn out to be the most efficient on .....
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RR-8560.pdf BibTex