Optilization of the gyroaverage operator based on hermite interpolation

TL;DR

This paper enhances the gyroaverage operator in gyrokinetic modeling by reformulating it as a matrix-vector product and optimizing the algorithm, significantly reducing computation time while maintaining accuracy.

Contribution

The paper introduces a reformulated, cache-friendly gyroaverage scheme based on Hermite interpolation, achieving over twofold speedup in computation.

Findings

Achieved more than twofold reduction in computation time.

Maintained accuracy of the gyroaverage operator.

Provided detailed algorithmic analysis and performance evaluation.

Abstract

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.