Re: FoF catalogue IDs

From: Weiguang Cui <cuiweiguang_at_gmail.com>
Date: Thu, 6 Jan 2022 20:17:06 +0000

Dear Volker,

Thank you for this reply. Now I understand. What about the outputs which
only have the most bound particles instead of a full snapshot? Are the IDs
from the "prevmostboundonly_" can be directly used as the IDs in the group
catalog?
I suppose so as they are "saved in group order", but just want to get
confirmation from you.

Best,
Weiguang

-------------------------------------------
https://weiguangcui.github.io/


On Thu, Jan 6, 2022 at 4:12 PM Volker Springel <
vspringel_at_mpa-garching.mpg.de> wrote:

>
> 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 21:17:54

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