Re: Merger Tree and restart flag 8

From: Volker Springel <vspringel_at_MPA-Garching.MPG.DE>
Date: Wed, 18 Aug 2021 11:40:21 +0200

Dear Suman,

> On 13. Aug 2021, at 13:47, Suman Chatterjee <sumanchttrj05_at_hotmail.com> wrote:
>
> Dear all,
> This is just a quarry regarding restart flag 8. The manual states :
> ".... one can ask GADGET-4 to isolate individual trees and to arrange the corresponding subhalos in a format that allows easy processing of the trees, for example, in a semi-analytic code for galaxy formation. This process also computes the other links shown in the above sketch. To this end, one starts GADGET-4 with restartflag 8 ...".
>
> If I understand correctly, if restart flag 8 is used, data will be arranged in tree-wise manner,

Yes, this is correct. This will produce the files in "treedata/*", in which subhalos belonging to a single trees are grouped together, and the links between (TreeFirstDescendant, TreeMainProgenitor,..., etc.) are expressed in terms of indices internal to the tree.


> may be like this :
> =====================
> "
> Tree2065:NXgroup Descendant = [-1 0 1] FileNr = [10 10 10] FirstHaloInFOFGroup = [0 1 2] FirstProgenitor = [ 1 2 -1] GroupCM = float32(3x3) GroupMassType = float32(3x6) Group_M_Crit200 = [0.269265 0.269265 0.26927 ] Group_M_Crit500 = [0.222053 0.237791 0.26927 ] Group_M_Mean200 = [0.365575 0.365588 0.349875] Group_M_TopHat200 = [0.332214 0.332214 0.334138] Group_R_Crit200 = [22.626024 22.774189 22.99517 ] Group_R_Crit500 = [15.633368 16.098663 16.943964] Group_R_Mean200 = [37.062725 37.06375 36.5244 ] Group_R_TopHat200 = [30.339376 30.454967 30.68801 ] NextHaloInFOFGroup = [-1 -1 -1] NextProgenitor = [-1 -1 -1] SnapNum = [99 98 97] .........
>
> Tree2066:NXgroup Descendant = -1 FileNr = 10 FirstHaloInFOFGroup = 0 FirstProgenitor = -1 GroupCM = [[ 4272.26 20351.26 14372.56]] GroupMassType = [[0.008101 0.472117 0. 0. 0. 0. ]] Group_M_Crit200 = 0.37769344449043274 Group_M_Crit500 = 0.2675328552722931 Group_M_Mean200 = 0.46446433663368225 Group_M_TopHat200 = 0.4450022876262665 Group_R_Crit200 = 25.32822036743164 Group_R_Crit500 = 16.6357364654541 Group_R_Mean200 = 40.14205551147461 Group_R_TopHat200 = 33.44480514526367 NextHaloInFOFGroup = -1 NextProgenitor = -1 SnapNum = 99 SubhaloBHMass = 0.0 SubhaloBHMdot = 0.0 SubhaloBfldDisk = 0.0 SubhaloBfldHalo = 0.0 ........
>
> and so on .... "
> =================
> However, the new tree-files that are generated by restart flag 8 are of similar structure as restart flag 7, i.e., :

Hmm, I guess I don't really understand this question. Restartflag 7 does not produce tree files. It does produce subhalo_desc/subhalo_prog files for individual group catalogues, linking two subsequent ones.

Best regards,
Volker



> =================
> TreeHalos:NXgroup GroupNr = int64(87002) Group_M_Crit200 = float32(87002) SnapNum = int32(87002) SubhaloHalfmassRad = float32(87002) SubhaloIDMostbound = uint32(87002) SubhaloLen = int32(87002) SubhaloMass = float32(87002) SubhaloNr = int64(87002) SubhaloPos = float32(87002x3) SubhaloSpin = float32(87002x3) SubhaloVel = float32(87002x3) SubhaloVelDisp = float32(87002) SubhaloVmax = float32(87002) SubhaloVmaxRad = float32(87002) TreeDescendant = int32(87002) TreeFirstDescendant = int32(87002) TreeFirstHaloInFOFgroup = int32(87002) TreeFirstProgenitor = int32(87002) TreeID = int64(87002) TreeIndex = int32(87002) TreeMainProgenitor = int32(87002) TreeNextDescendant = int32(87002) TreeNextHaloInFOFgroup = int32(87002) TreeNextProgenitor = int32(87002) TreeProgenitor = int32(87002) TreeTable:NXgroup Length = int32(18467) StartOffset = int64(18467) TreeID = int64(18467) TreeTimes:NXgroup Redsh
ift = float64(4) Time = float64(4)
> =========================
>
> Maybe I am missing something. It would helpful if you would point me towards the correct understanding.
>
>
> Regards,
> Suman Chatterjee
> NCRA-TIFR, Pune
>
>
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Received on 2021-08-18 11:40:23

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