Bibcode
DOI
Trujillo Bueno, J.; Fabiani Bendicho, P.
Bibliographical reference
Astrophysical Journal v.455, p.646
Advertised on:
12
1995
Citations
97
Refereed citations
70
Description
Iterative schemes based on Gauss-Seidel (G-S) and optimal successive
over-relaxation (SOR) iteration are shown to provide a dramatic increase
in the speed with which non-LTE radiation transfer (RT) problems can be
solved. The convergence rates of these new RT methods are identical to
those of upper triangular nonlocal approximate operator splitting
techniques, but the computing time per iteration and the memory
requirements are similar to those of a local operator splitting method.
In addition to these properties, both methods are particularly suitable
for multidimensional geometry, since they neither require the actual
construction of nonlocal approximate operators nor the application of
any matrix inversion procedure.
Compared with the currently used Jacobi technique, which is based on the
optimal local approximate operator (see Olson, Auer, & Buchler
1986), the G-S method presented here is faster by a factor 2. It gives
excellent smoothing of the high-frequency error components, which makes
it the iterative scheme of choice for multigrid radiative transfer. This
G-S method can also be suitably combined with standard acceleration
techniques to achieve even higher performance.
Although the convergence rate of the optimal SOR scheme developed here
for solving non-LTE RT problems is much higher than G-S, the computing
time per iteration is also minimal, i.e., virtually identical to that of
a local operator splitting method. While the conventional optimal local
operator scheme provides the converged solution after a total CPU time
(measured in arbitrary units) approximately equal to the number n of
points per decade of optical depth, the time needed by this new method
based on the optimal SOR iterations is only √n/2√2. This
method is competitive with those that result from combining the
above-mentioned Jacobi and G-S schemes with the best acceleration
techniques.
Contrary to what happens with the local operator splitting strategy
currently in use, these novel methods remain effective even under
extreme non-LTE conditions in very fine grids.