#1

=cmcsc10 =cmdunh10 at 12.0 true pt =cmdunh10 =cmbx10 scaled 1 =cmbx7 =cmti7 =cmr17

=0

1Dept. of Physics and Astronomy, University of Oklahoma, 440 W. Brooks, Rm 131, Norman, OK 73019-0225; baron@mail.nhn.ou.edu

2Dept. of Physics and Astronomy & Center for Simulational Physics, University of Georgia, Athens, GA 30602-2451; yeti@hal.physast.uga.edu

Sept. 21, 1997

We describe an important addition to the parallel implementation of
our generalized NLTE stellar atmosphere and radiative transfer computer
program `PHOENIX`. In a previous paper in this series we described data
and task parallel algorithms we have developed for radiative transfer,
spectral line opacity, and NLTE opacity and rate calculations.
These algorithms divided the work spatially or by spectral lines,
that is distributing the radial zones, individual spectral lines,
or characteristic rays among different processors and employ, in
addition task parallelism for logically independent functions (such as
atomic and molecular line opacities). For finite, monotonic velocity
fields, the radiative transfer equation is an initial value problem in
wavelength, and hence each wavelength point depends upon the previous
one. However, for sophisticated NLTE models of both static and moving
atmospheres needed to accurately describe, e.g., novae and supernovae,
the number of wavelength points is very large (200,000-300,000) and hence
parallelization over wavelength can lead both to considerable speedup
in calculation time and the ability to make use of the aggregate memory
available on massively parallel supercomputers. Here, we describe an
implementation of a pipelined design for the wavelength parallelization
of `PHOENIX`, where the necessary data from the processor working on
a previous wavelength point is sent to the processor working on the
succeeding wavelength point as soon as it is known. Our implementation
uses a MIMD design based on a relatively small number of standard `MPI` library calls and is fully portable between serial and parallel computers.

- Introduction
- Equations and Problem Description
- Wavelength Parallelization
- Results of performance tests
- Summary and Conclusions
- References
- About this document ...