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

[tazkera haque]

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
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