Hi Stefan, I have been contemplating changes to the MC codes. One thing we have found is that MCGeneral breaks down when Q starts to get large. We see unrealistic results at 684 GHz when using horizontally aligned particles with high aspect ratio. Yuli Liu, who is working with us now, did comprehensive analysis, and we believe that the issue is the way the backwards algorithm is using importance sampling to avoid the issue of inverting the extinction matrix; however, this approach neglects the mixing of I and Q. I believe this is a simple fix.
The other issue is that MCGeneral is not very ARTS-like. Looking at the way it is structured, I think a better approach would be to have an iyMC that traces a single "photon," and yMC would integrate these individual results. Random sampling of both the antenna pattern and the bandwidth could be performed at this level. I also think that the MC sampled antenna pattern could be more widely useful across ARTS. These papers provide an interesting curveball. The ARTS MC codes are particularly slow, and they are not optimized for optically thin or extremely optically thick atmospheres. We could look at using these libraries, or at least techniques, but I'm not sure how intensive such a restructuring of the code would be. Of course, the tricky piece here is finding someone with the time to do this work. But, I think these changes would make the codes significantly more usable, and hopefully therefore used. Cheers, Ian On 11/29/23, 11:22 AM, "arts_dev.mi on behalf of Stefan Buehler" <arts_dev.mi-boun...@lists.uni-hamburg.de <mailto:arts_dev.mi-boun...@lists.uni-hamburg.de> on behalf of stefan.bueh...@uni-hamburg.de <mailto:stefan.bueh...@uni-hamburg.de>> wrote: Dear all, I stumbled accross this interesting paper on an open C library for particularly efficient MC calculations. Could this be the basis of ARTS 3D MC flux and heating rate calculations? Using MC sampling also for the spectral dimension, to be efficient, as in the second paper, which is also impressive, I think. They use MC sampling even for the spectral lines, if I got it right! (Basically treating each transition as if it were its own absorption species.) /Stefan https://www.dropbox.com/scl/fi/smsisfgc2it3sx4gov970/J-Adv-Model-Earth-Syst-2019-Villefranque-A-Path-E2-80-90Tracing-Monte-Carlo-Library-for-3-E2-80-90D-Radiative-Transfer-in-Highly.pdf?rlkey=v5yvrm64fnljaf739j4ssllux&dl=0 <https://www.dropbox.com/scl/fi/smsisfgc2it3sx4gov970/J-Adv-Model-Earth-Syst-2019-Villefranque-A-Path-E2-80-90Tracing-Monte-Carlo-Library-for-3-E2-80-90D-Radiative-Transfer-in-Highly.pdf?rlkey=v5yvrm64fnljaf739j4ssllux&dl=0> https://www.dropbox.com/scl/fi/r1tm3jdzx57kb85nowmt0/Yaniss_ea_PNAS_2023_smi.pdf?rlkey=8d4a7rb4u8pehckawbfk08c9f&dl=0 <https://www.dropbox.com/scl/fi/r1tm3jdzx57kb85nowmt0/Yaniss_ea_PNAS_2023_smi.pdf?rlkey=8d4a7rb4u8pehckawbfk08c9f&dl=0>
