[yt-users] defining derived field only for Gas particles

Wed Oct 4 10:03:25 PDT 2017

Hi Prateek and Ari,

Thanks very much for your feedback. I took your suggestion and I figured
out my problem. It's all about making the new derived field units in  'g'.
As a correction, I changed the unit to 'code_mass' to get the right order
of magnitude for my new field. The only reason I cannot do
dd[“Gas’,’Mass’].in_units(‘g’)
because it does not take into account some constant correction for my
simulation. so the code with correct magnitude now looks like this:

def _PhysicalMass(field, data):
    return data['Gas','Mass']*((5995.*(1e10)*(1.98855e33))/(0.7))
ds.add_field(("gas", "PhysicalMass"), function=_PhysicalMass,
units="code_mass")

so now dd["gas", "PhysicalMass"] returns the right magnitude. The unit is
still in 'code_mass' but It is technically converted into gram.

Thanks very much for your time

Best
Tazkera

On Wed, Oct 4, 2017 at 10:50 AM, Ari Maller <AMaller at citytech.cuny.edu>
wrote:

> It is a little unclear why you are trying to do what you are doing.
>
> To convert unit systems in yt there are a bunch of unit commands. For
> example
> dd[“Gas’,’Mass’].in_units(‘g’)
> would return the masses in grams.
>
> I think what is going wrong in your derived field is that you set the
> units to grams and then add your conversion factor to that, but you wanted
> to use your conversion factor on the code masses. If you just want Physical
> mass to be in grams and no extra conversion then you could set the units to
> grams and do nothing to the array.
>
> The first question is whether yt internal unit conversion is working
> correctly for you or not. Gadget does not output Tipsy files, so it is
> possible the frontend is doing something wrong since your data sounds very
> unusual.  If you need some extra conversion then you can see what the
> values of your Masses are in the units of your choice and then add derived
> field in those units that makes the extra conversion.
>
> Ari
>
>
> > On Oct 3, 2017, at 11:53 PM, yt-users-request at lists.spacepope.org wrote:
> >
> > Send yt-users mailing list submissions to
> >       yt-users at lists.spacepope.org
> >
> > To subscribe or unsubscribe via the World Wide Web, visit
> >       http://lists.spacepope.org/listinfo.cgi/yt-users-spacepope.org
> > or, via email, send a message with subject or body 'help' to
> >       yt-users-request at lists.spacepope.org
> >
> > You can reach the person managing the list at
> >       yt-users-owner at lists.spacepope.org
> >
> > When replying, please edit your Subject line so it is more specific
> > than "Re: Contents of yt-users digest..."
> >
> >
> > Today's Topics:
> >
> >   1. defining derived field only for Gas particles (tazkera haque)
> >
> >
> > ----------------------------------------------------------------------
> >
> > Message: 1
> > Date: Tue, 3 Oct 2017 23:29:31 -0400
> > From: tazkera haque <h.tazkera at gmail.com>
> > To: Discussion of the yt analysis package
> >       <yt-users at lists.spacepope.org>
> > Subject: [yt-users] defining derived field only for Gas particles
> > Message-ID:
> >       <CAFj_7zyiZYPOWuFPsPtbGtNVDvXF9G3Z+1srY_TvDKrFM8oRkg at mail.gmail.
> com>
> > Content-Type: text/plain; charset="utf-8"
> >
> > Dear yt community,
> >
> > I am analyzing some Tipsy data output from Gadget 3. I have three
> different
> > particles, Gas, Star and Dark Matter. I want to derive a new field
> > 'PhysicalMass', that will make a unit conversion of code_mass to some
> > physical mass units. My code so far looks like this:
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > *import ytfrom yt import derived_field at derived_field(
> name="PhysicalMass",
> > units="g")def _PhysicalMass(field, data):    M =
> > data['Gas','Mass']*((5995.*(1e10)*(1.98855e33))/(0.7))    return Mds =
> > yt.load('snap_p6n36fof_031.bin', n_ref=64)dd= ds.all_data*
> >
> >
> > My default ('Gas', 'Mass') array looks like this:
> > *dd['Gas','Mass']*
> >
> > YTArray([  9.64448986e-07,   9.64448986e-07,   9.64448986e-07, ...,
> >         9.64448986e-07,   9.64448986e-07,   9.64448986e-07]) code_mass
> >
> > But when I call the new derived field, it takes some values which does
> > not correspond to the conversion constants I have multiplied with:
> >
> > dd['PhysicalMass']
> > YTArray([  3.26598467e+74,   3.26598467e+74,   3.26598467e+74, ...,
> >         3.26598467e+74,   3.26598467e+74,   3.26598467e+74]) g
> >
> > I can directly multiply the ('Gas', 'Mass') array with some conversion
> > factors to get accurate values, but I need to define a new field for
> > later calls:
> > dd['Gas','Mass']*((5995.*(1e10)*(1.98855e33))/(0.7))
> >
> >
> >
> > So my question is how do I get a new field which will only contain
> > PhysicalMass from Gas particles. it seems dd['Gas', 'PhysicalMass'] does
> > not exist.
> >
> >
> > Thanks very much for your time.
> >
> > Best
> > Tazkera
> > -------------- next part --------------
> > An HTML attachment was scrubbed...
> > URL: <http://lists.spacepope.org/pipermail/yt-users-spacepope.
> org/attachments/20171003/d9ee4086/attachment.html>
> >
> > ------------------------------
> >
> > Subject: Digest Footer
> >
> > _______________________________________________
> > yt-users mailing list
> > yt-users at lists.spacepope.org
> > http://lists.spacepope.org/listinfo.cgi/yt-users-spacepope.org
> >
> >
> > ------------------------------
> >
> > End of yt-users Digest, Vol 116, Issue 1
> > ****************************************
>
> _______________________________________________
> yt-users mailing list
> yt-users at lists.spacepope.org
> http://lists.spacepope.org/listinfo.cgi/yt-users-spacepope.org
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.spacepope.org/pipermail/yt-users-spacepope.org/attachments/20171004/c7ee7b6a/attachment-0001.html>