Re: Some setups about on-the-fly lightcones

From: Volker Springel <vspringel_at_MPA-Garching.MPG.DE>
Date: Thu, 5 Jan 2023 14:08:20 +0100

Hi Zhao,

> On 27. Dec 2022, at 14:10, 陈钊 <> wrote:
> Dear all,
> I am trying to use Gadget4 to generate on-the-fly lightcones for weak lensing studies. The main products I want are the halo lightcones and mass maps. However, I found that those saved mass maps are empty if the ‘LIGHTCONE_PARTICLES’ is not activated and with ‘LIGHTCONE_MASSMAPS’ activated alone. Is this set by definition or some extra setups is needed?

I can confirm, LIGHTCONE_MASSMAPS produced empty mass maps if LIGHTCONE_PARTICLES has not been activated as well. This was because of an initialization problem if only the first option was set. I have now fixed this in the code, i.e. it should now work.

> At the same time, the snapshots must be at the exact redshifts for my study so I need to activate the “OUTPUT_NON_SYNCHRONIZED_ALLOWED” which means that the halo can only be calculated by post-processing. Is there some setups to make Gadget4 can post-process the particle lightcones and obtain the halo lightcones? I don’t find something about this in the document.

No, at the moment there is no built-in option to load the lightcone particle data and run the group finder on it in postprocessing (unlike for snapshots, where this is readily possible). In practice, this would typically be very difficult for memory reasons - normally the particle lightcone data is much bigger than a single snapshot, so running the halo finder in one go on it would not be possible. This could only be circumvented by piecing things together somehow. If your lightcone is small enough, you can in principle accumlate the lightcone data and store it as a mock snapshot file, and then run the group finder on it.

> At last, when I test some runs by using small box (250 Mac/h) to generate particle lightcones at high redshift (z~3.0), I config ‘LIGHTCONE_MAX_BOXREPLICAS=100000’, ‘LIGHTCONE_PARTICLES’, ‘LIGHTCONE_PARTICLES_GROUPS’ and without ’non_syn’. But I got strange exit code shown as follows:
> [[[Code termination on task=3645, function fof_compile_catalogue(), file src/fof/, line 595: start=331118 i=447801 Tp->NumPart=807400 FOF_GList[start].DistanceOrigin=4449.11 != FOF_GList[i].DistanceOrigin=4452.7 MinID=695628668 MinIDTask=3528]]]
> Does anyone knows what’s this error means? And what I need to modify the config file or something else?

This error should not occur... I think it has been due to a small glitch in the LIGHTCONE_PARTICLES_GROUPS option, which I now fixed. If the error should still occur, please send me your full setup so that I can try to reproduce it.


> Thanks for your time in advance!
> Best,
> Zhao
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Received on 2023-01-05 14:08:21

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