Optimization of the gyroaverage operator based on hermite interpolation

Fabien Rozar (1, 2, 3) , Christophe Steiner (4) , Guillaume Latu (3) , Michel Mehrenberger (5, 4) , Virginie Grandgirard (3) , Julien Bigot (6) , T Cartier-Michaud (3) , Jean Roman (2)

1 LaBRI - Laboratoire Bordelais de Recherche en Informatique
2 HiePACS - High-End Parallel Algorithms for Challenging Numerical Simulations
3 IRFM - Institut de Recherche sur la Fusion par confinement Magnétique
4 IRMA - Institut de Recherche Mathématique Avancée
5 TONUS - TOkamaks and NUmerical Simulations
6 MDLS - Maison de la Simulation

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.

Mots clés: Optimisation; Hermite Interpolation; Data structure; Plasma physics

Domaines: Calcul parallèle, distribué et partagé [cs.DC]; Algorithme et structure de données [cs.DS]; Modélisation et simulation; Physique mathématique [math-ph]

Fabien Rozar, Christophe Steiner, Guillaume Latu, Michel Mehrenberger, Virginie Grandgirard, et al.. Optimization of the gyroaverage operator based on hermite interpolation. ESAIM: Proceedings and Surveys, 2016, ⟨10.1051/proc/201653012⟩. ⟨hal-01261427⟩