[yt-users] adding quantities to halo catalogs

[Britton Smith]

Hi Ari,

I suggest something like the following.  First, you need to define a data
container to associate with each halo.  This is usually a sphere, and you
can follow the cookbook recipe for how to do that:
http://yt-project.org/doc/cookbook/cosmological_analysis.html#halo-profiling-and-custom-analysis

If you use the "sphere" callback as the example above shows, it will create
a sphere data container associated with each halo object as:
halo.data_container

Then, assuming you have your cold_gas_mass field, you can just define a
quantity that returns the total of that over the halo's sphere.  The sphere
object is like any other data container, so you can use a derived quantity
to return the total of your field.  It should look something like this:

def _total_cold_gas(halo):
    return halo.data_container.quantities.total_quantity("cold_gas_mass")
add_quantity("total_cold_gas", _total_cold_gas)

Let us know if you encounter any troubles and thanks for pointing out some
places where the docs could use some additions!

Britton

On Mon, Jun 22, 2015 at 9:41 PM, Professor Maller <amaller at citytech.cuny.edu
> wrote:

> Hi Everyone,
>
> I'm trying to add a quantity to my halo catalog which is cold gas mass. We
> can assume I've already defined the field cold_gas_mass, but I'm having
> trouble understanding how to add it to my halo catalog. The examples all
> seem to be for profiles and it isn't clear to me what to do if you aren't
> looking for a profile. Does anyone have an example of doing something like
> this they could share?  The total gas mass or any other sum of fluid
> quantities would probably be close enough for me understand the syntax.
>
> Thanks,
>
> Ari
>
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