Add facility to patch trees where halos (esp subhalos) get 'lost' by halo finder #192
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…instabilities, a little like a simple version of Behroozi's consistent-trees
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…wise may get in the way of patching trees
* prune-trees: Add minimum (as well as maximum) bound on NDM of a progenitor * prune-trees: Improve clarity of query * patch-trees: Make position offset sphere a comoving radius, to improve identifications at high redshift * patch-trees: Search over more timesteps by default * patch-trees: Cache gathered information about halos in timestep to improve performance
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A common problem, especially when dealing with subhalos, is that on some steps even the best halo finder will 'lose' the halo. This completely messes up the merger tree, as things stand.
I am adding here a tool that can start to address this issue. For instance I have tried it with
Halo685_AHF.db(@Martin-Rey @gandhalij) and, bearing in mind how simple it is, it does seem to help a little bit.The first step is to remove suspect links (e.g. where the major progenitor of a subhalo is identified as the parent halo, because the subhalo was temporarily lost):
tangos --db-filename Halo685_AHF.db prune-treesHaving done this, you can then try to find sensible links for cases where no progenitor has been identified
tangos --db-filename Halo685_AHF.db patch-trees --include-only 'NStar()>100' 'NDM()>100' 'contamination_fraction<0.01'Parameters to play with here:
--relative-matchcurrentlyNStar()andNDM(), meaning the changes in these quantities are checked--max-for-matchcurrently 0.1, meaning a 10% change in these key quantities are allowed to qualify for a match--max-position-offsetcurrently 100, meaning a 100kpc comoving offset allowed to qualify for a match--max-timestepscurrently 6, meaning how many steps back in time a possible progenitor is soughtFeedback would be much appreciated...