Numerical non-LTE 3D radiative transfer using a multigrid method
Title:
Numerical non-LTE 3D radiative transfer using a multigrid method
Authors:
Bjørgen, Johan P.; Leenaarts, Jorrit
Publication:
eprint arXiv:1701.01607
Publication Date:
01/2017
Origin:
ARXIV
Keywords:
Astrophysics - Solar and Stellar Astrophysics, Astrophysics - Instrumentation and Methods for Astrophysics
Comment:
Accepted for publication by A&A
Bibliographic Code:
2017arXiv170101607B
Abstract
3D non-LTE radiative transfer problems are computationally demanding, and this
sets limits on the size of the problems that can be solved. So far Multilevel
Accelerated Lambda Iteration (MALI) has been to the method of choice to perform
high-resolution computations in multidimensional problems. The disadvantage of
MALI is that its computing time scales as $\mathcal{O}(n^2)$, with $n$ the number
of grid points. When the grid gets finer, the computational cost increases
quadratically. We aim to develop a 3D non-LTE radiative transfer code that is more
efficient than MALI. We implement a non-linear multigrid, fast approximation storage
scheme, into the existing Multi3D radiative transfer code. We verify our multigrid
implementation by comparing with MALI computations. We show that multigrid can
be employed in realistic problems with snapshots from 3D radiative-MHD
simulations as input atmospheres. With multigrid, we obtain a factor 3.3-4.5
speedup compared to MALI. With full-multigrid the speed-up increases to a factor 6.
The speedup is expected to increase for input atmospheres with more grid points
and finer grid spacing. Solving 3D non-LTE radiative transfer problems using non-
linear multigrid methods can be applied to realistic atmospheres with a substantial
speed-up.