Re: FoF catalogue IDs

From: Volker Springel <vspringel_at_MPA-Garching.MPG.DE>
Date: Thu, 6 Jan 2022 17:11:07 +0100

Dear Weiguang,

Yes, the IDs of group particles are not saved any more in the group catalogues, as this information is redundant - the particle ID block in the snapshot files contains the *identical* information, because the particles are stored in group order by default (except that at the end of the snapshot ID block, also particle IDs not contained in any group are listed).

The gadget4 code still contains the function fof_subfind_prepare_ID_list() necessary to prepare the IDs such that they can also be added to the group catalogue itself. In the public Arepo code, this option is still there (with the FOF_STOREIDS switch), and it could be reenabled for Gadget4, if desired, by again adding the lines enabled by this switch. However, as I said, it was deliberately removed in Gadget4 as being redundant.

Best,
Volker

> On 5. Jan 2022, at 14:28, Weiguang Cui <cuiweiguang_at_gmail.com> wrote:
>
> Dear all,
>
> It seems the particle IDs for the FoF groups are not saved in the output FoF catalog...
> ```
> [_at_login8a groups_301]$ h5dump -g IDs fof_subhalo_tab_301.0.hdf5
> HDF5 "fof_subhalo_tab_301.0.hdf5" {
> GROUP "IDs" {
> }
> }
> ```
> Is this because of any configure or parameter options that I forgot to set for outputting this information? Or the `GroupOffsetType` and `GroupLenType` can be directly applied to the snapshot files?
> Thank you!
>
> Best,
> Weiguang
>
> -------------------------------------------
> https://weiguangcui.github.io/
>
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Received on 2022-01-06 17:11:08

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