On Thu, Oct 12, 2017 at 9:33 AM, ｔyuta <y0u1t1a5.t@gmail.com> wrote:
Dear Nathan,

The particle filter worked well and I could read the star density from the data. Thanks!
Now I want to subtract stellar mass density from Dark_Matter_Density. I was trying to define a new field "only_DM", but it did not work. Could you tell me what is wrong with this?

(jupiter notebook session)
import yt
from yt.data_objects.particle_filters import add_particle_filter

def stars(pfilter, data):
    filter = data[(pfilter.filtered_type, "particle_type")] == 2
    return filter

add_particle_filter("stars", function=stars, filtered_type='io',
                    requires=["particle_type"])

ds.add_particle_filter('stars')

def only_DM(field, data):
    return data['Dark_Matter_Density'] - data['deposit','stars_density']

ds=yt.load(".../redshift00??")

ds.add_field(("Dark_Matter_Density", "only_DM_Density"), units="kg/m**3", function=only_DM)

The issue might be here? I think this field needs to be named ('gas', 'only_DM_density') - the field entry in a yt field tuple is always a field type, not a field name as you've used here. You need to use the 'gas' field type because it's defined on the Enzo AMR mesh, which is usually only for gas fields.

You might also want to try using a particle filter for the dark matter as well, dark matter particles have particle_type == 0.

-Nathan
 

and the error message appears:
YTFieldNotFound: Could not find field '('deposit', 'stars_density')' in redshift00??.

Sincerely,
Y.T.

2017-10-11 16:24 GMT-04:00 Nathan Goldbaum <nathan12343@gmail.com>:
OK, in that case I wouldn't try to infer the stellar mass from the Dark_Matter_Density field (which does include stellar mass despite the name), instead I would define a particle filter for stars (http://yt-project.org/doc/analyzing/filtering.html#filtering-particle-fields) and then use the new particle type defined by the filter to create a deposited particle field (http://yt-project.org/doc/analyzing/fields.html#deposited-particle-fields).

There's an example in the docs for how to do this with Tipsy data here: http://yt-project.org/doc/cookbook/constructing_data_objects.html#creating-particle-filters

For Enzo, you should use the particle_type field to create the filter - star particles in Enzo have particle_type equal to 2. Here's a short worked example:


Hope that helps! And I hope to hear more from you - your name is particularly well suited to the yt project ;)

-Nathan


On Wed, Oct 11, 2017 at 12:58 PM, ｔyuta <y0u1t1a5.t@gmail.com> wrote:
Yes, it's Enzo data.

2017-10-11 10:17 GMT-04:00 Nathan Goldbaum <nathan12343@gmail.com>:
What simulation code are you working with? From the field names it sounds like Enzo data.

On Wed, Oct 11, 2017 at 9:13 AM ｔyuta <y0u1t1a5.t@gmail.com> wrote:
Dear yt-users,

Hi, I'm a new user of yt. I have a question about the default 'Density' field and 'Dark_Matter_Density' field. Do they contain stellar mass? If so, how can I read and subtract stellar mass from the data?

Sincerely,
Y.T.
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