Geodesic
Optimization of the Gyroaverage operator based on Hermite interpolation
Fabien Rozar1, 2 ; Christophe Steiner3 ; Guillaume Latu2 ; Michel Mehrenberger3 ; Virginie Grandgirard2 ; Julien Bigot1 ; Thomas Cartier-Michaud2 ; Jean Roman4
1 Maison de la Simulation, USR 3441, CEA / CNRS / Inria / Univ. Paris-Sud / Univ. Versailles, 91191 Gif-sur-Yvette, FRANCE
2 CEA, IRFM, F-13108 Saint-Paul-lez-Durance
3 IRMA, Université de Strasbourg, France
4 Inria, Bordeaux INP, CNRS, FR-33405 Talence
ESAIM. Proceedings, Tome 53 (2016), pp. 191-210.

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Gyrokinetic modeling is appropriate for describing Tokamak plasma turbulence, and the gyroaverage operator is a cornerstone of this approach. In a gyrokinetic code, the gyroaveraging scheme needs to be accurate enough to avoid spoiling the data but also requires a low computation cost because it is applied often on the main unknown, the 5D guiding-center distribution function, and on the 3D electric potentials. In the present paper, we improve a gyroaverage scheme based on Hermite interpolation used in the Gysela code. This initial implementation represents a too large fraction of the total execution time. The gyroaverage operator has been reformulated and is now expressed as a matrix-vector product and a cache-friendly algorithm has been setup. Different techniques have been investigated to quicken the computations by more than a factor two. Description of the algorithms is given, together with an analysis of the achieved performance.
DOI : 10.1051/proc/201653012

Fabien Rozar 1, 2 ; Christophe Steiner 3 ; Guillaume Latu 2 ; Michel Mehrenberger 3 ; Virginie Grandgirard 2 ; Julien Bigot 1 ; Thomas Cartier-Michaud 2 ; Jean Roman 4

1 Maison de la Simulation, USR 3441, CEA / CNRS / Inria / Univ. Paris-Sud / Univ. Versailles, 91191 Gif-sur-Yvette, FRANCE
2 CEA, IRFM, F-13108 Saint-Paul-lez-Durance
3 IRMA, Université de Strasbourg, France
4 Inria, Bordeaux INP, CNRS, FR-33405 Talence 
@article{EP_2016_53_a12,
     author = {Fabien Rozar and Christophe Steiner and Guillaume Latu and Michel Mehrenberger and Virginie Grandgirard and Julien Bigot and Thomas Cartier-Michaud and Jean Roman},
     title = {Optimization of the {Gyroaverage} operator based on {Hermite} interpolation},
     journal = {ESAIM. Proceedings},
     pages = {191--210},
     publisher = {mathdoc},
     volume = {53},
     year = {2016},
     doi = {10.1051/proc/201653012},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.1051/proc/201653012/}
}
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%A Guillaume Latu
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%A Thomas Cartier-Michaud
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Fabien Rozar; Christophe Steiner; Guillaume Latu; Michel Mehrenberger; Virginie Grandgirard; Julien Bigot; Thomas Cartier-Michaud; Jean Roman. Optimization of the Gyroaverage operator based on Hermite interpolation. ESAIM. Proceedings, Tome 53 (2016), pp. 191-210. doi : 10.1051/proc/201653012. http://geodesic.mathdoc.fr/articles/10.1051/proc/201653012/

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