Fwd: [Sunrise] Sunrise v4.0 release!
This might be of interest to people here. Congratulations to Patrik and the other developers! This is a very impressive accomplishment.
---------- Forwarded message ---------- From: Patrik Jonsson email@example.com Date: Wed, May 9, 2012 at 1:56 PM Subject: [Sunrise] Sunrise v4.0 release! To: firstname.lastname@example.org
Hi Sunrise users,
I'm pleased to announce the release of the long-in-the-making Sunrise v4.0!
This new version includes many updates, and a paper describing them is in the works. (However, it will likely be a while until this paper is done, for reasons that will become obvious below.) Special thanks should go to Chris Moody and Greg Snyder, who have done a lot of work testing the new versions and finding bugs. You can get the version now by using the tag "v4_00" in the Mercurial repository.
One of the most exciting ones is the support for distributed-memory machines using MPI. This means that you no longer will have to go hunting for machines with extremely large memory to run Sunrise on large simulations. (However, the overhead for running MPI is quite high, so it is not useful for speeding up small calculations.) See the "Using MPI" Wiki page (http://code.google.com/p/sunrise/wiki/UsingMPI) for more information. The MPI functionality works but has not been extensively tested, so you are likely to run into bugs. Please report any issues that arise.
A prerequisite for getting the MPI version to work was to redo the way the adaptive mesh works. The grid is now a pure octree, meaning it always starts with one root cell that is then recursively subdivided into octants. Before, the root grid was a cartesian grid of arbitrary size, but that is no longer supported. (This was necessary to get the Hilbert ordering of the cells used for domain decomposition working efficiently.) This new grid is also more efficient than the old version.
The calculation of infrared emission has also been redone. When finding the equilibrium dust temperatures/radiation fields, it now uses the "immediate reemission" method described in Fleck & Cummings (1971) and Lucy (1999). This exactly preserves the energy balance when grains absorb/reemit photons, and discretizes only the temperature field (not the radiation intensity) on the grid when iterating, which should give better accuracy at a given grid resolution.
Finally, instead of MC sampling the emission distribution in the cells when making images of dust emission, the direct emission is now calculated by explicitly integrating the RTE along the line of sight. This results in nose-free images. The scattered light is still done with MC, but at the wavelengths where the dust emission dominates, the albedo is essentially zero anyway so this doesn't make much difference. The integration is adaptive in the sense that the size of the cells encountered are monitored, and if the cells are smaller than the solid angle subtended by the ray, the ray is subdivided (similar to what Abel & Wandelt 99 did, but for incoming rays as opposed to outgoing ones).
Furthermore, an explicit monitoring of Monte Carlo error in the iteration, which adjusts the number of rays to achieve the specified accuracy, has been included. The previous method of testing convergence did not guarantee an accurate temperature field, only that the overall energy balance was within a certain limit. The new method monitors the error in determining the temperature of each individual cell. The flipside is that if you ask for a high accuracy, you'd better be prepared to wait a *long* time. The full force of the sqrt(N) Monte Carlo convergence rate will hit you.
The polychromatic ray tracing algorithm has been upgraded with an automatic determination of reference wavelength and forced scattering positions to avoid large bias factors in situations with high optical depths. Instead of splitting rays that have been boosted to high intensities after the fact, it avoids large bias factors in the first place by forcing several scatterings along the line of propagation. This lowers the noise caused by the large bias factors and avoids the guesswork in setting the reference wavelength and forced scattering parameters.
There are also many efficiency tweaks that have sped up the calculation. (However, the most important factor affecting runtime, by far, is the dust equilibrium accuracy required.) The code is capable of processing snapshots from Gadget, Gasoline, Arepo, and, using YT to export files, from Enzo and ART. If you are interested in the YT functionality, contact Matt Turk and he can point you in the right direction. I don't know anything about how the YT export works.
Finally, Sunrise now handles kinematics, meaning that it can take into account the effect of velocity and Doppler shift of sources and scatterers. However, for this to work you need a SED library with logarithmic wavelength spacing (and for it to be useful, quite high resolution). A high-resolution set of Starburst99 and MAPPINGS files have been uploaded to the Downloads section of the Sunrise web site. Note that with such high spectral resolution, maintaining high spatial resolution comes at the cost of *very* large memory use and output file size. It's best to cut out a small wavelength range around the features you are interested in. (And don't even think of calculating dust emission with that wavelength resolution...)
For those of you who are interested in knowing more about what's happening inside the galaxy, there are also now options to save the dust emission SEDs and the dust temperatures to the output file.
All these changes naturally means that parameter keywords have changed. I'll post another message containing example configurations, but I encourage you to carefully read through the Wiki pages describing the keywords to get an idea of the changes. As usual, you have to take responsibility for verifying that the results make sense, so don't just take the example files without actually verifying that things work correctly in your particular situation. The library requirements have also changed, so review the compilation instructions and be sure to update your copy of libPJutil from the repo at https://bitbucket.org/lutorm/libpjutil.
The other big update is that I will no longer be working primarily on Sunrise. Next week, I'm moving to a position as software engineer at SpaceX in LA, working on simulation software for rockets! :-) I will still have my research grant for the next few years, but I'm unlikely to have much time to work on astrophysics. Chris Hayward, who has worked a lot with Sunrise, has graciously accepted taking over as the primary maintainer of the code. However, everyone will have to help Chris by pitching in with tracking down bugs you find, and with providing improvements. You are still welcome to email me with questions, but I should probably not be the first choice as my ping time is likely to be very long.
I hope that all the effort I've put into Sunrise over the years will continue to be built on so Sunrise will remain the premier tool in galaxy SED prediction!
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