[Yt-dev] filters for DerivedQuantities

[Sam Skillman]

Hi John,

I think you could also do something similar with a 1D profile, though it
isn't quite as easy to dial in an exact limit:

http://yt.enzotools.org/doc/api/generated/plot_types/yt.raven.PlotCollection.add_profile_object.html?highlight=add_profile#yt-raven-plotcollection-add-profile-object

where you define the whole box as the region you care about and then do:
# Get the whole box
reg = pf.h.all_data()

# Make the profile
metal_mass = pc.add_profile_object(reg, ["Metallicity", "CellMass"])

# Get some easy pointers to the profile data
bins = metal_mass.data._bins
mass = metal_mass.data["CellMass"]

#  Now get total mass with Metallicity above a 1.0e-4 by getting the number
of
mass_frac = mass[bins>1.0e-4].sum()/mass.sum()

That should give you something close to what you'd want.  You may want to
increase the number of xbins if you want higher accuracy answer.  Finally,
I'll just make a quick note that the profile creation can be done in
parallel as long as lazy_reader=True, which it is by default.

There may be other ways to do this as well, but this is what I'd probably
do.

Best,
Sam

On Thu, Aug 26, 2010 at 7:00 AM, John Wise <jwise at astro.princeton.edu>wrote:

> Hi,
>
> I wanted to calculate volume filling fractions and mass fractions of gas
> that met some criteria.  Specifically, the fractions that have a certain
> metallicity.  The _Action routine looked promising, but I couldn't figure
> out how to use it.  I remember there was some talk about filters on the
> list, but I searched and found that it concerned the halo finder.
>
> I might have reinvented the wheel, but this is how I did it.
>
> http://paste.enzotools.org/show/1125/
>
> It's basically _TotalQuantity with a filter.  Also I wanted it to accept
> multiple limits to avoid re-reading the data for every filter.
>
> Was there an easier way to do this?
>
> Thanks,
> John
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>



-- 
Samuel W. Skillman
DOE Computational Science Graduate Fellow
Center for Astrophysics and Space Astronomy
University of Colorado at Boulder
samuel.skillman[at]colorado.edu
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