[yt-users] Confused about units in derived fields

Jill Naiman jill.naiman at cfa.harvard.edu
Thu Nov 20 18:27:09 PST 2014


Hi all,

As the title states, I am confused - specifically about units.  I want to
create a derived field where parts of the field are different values,
dependent upon some cutoff criteria like so:

def _dene2(field,data):
    tl = data['temperature']
    dl = data['density']
    print("TEMP")
    print(tl.in_cgs())
    aux = np.where(tl.in_cgs() > 5000.)
    np.putmask(dl,aux, 0.0)
    dene = dl
    return dene


ds.add_field("dene", units="g/cm**3", function = _dene2)


Not only does this produce a very worrisome error:  "RuntimeError:
Something has gone terribly wrong, _function is NullFunc for ('flash',
'temp')"

The print statement in there shows a bunch of values close to 1, which is
why the "aux" mask never returns anything.  But why is data a bunch of 1's
in here?  How do I access/convert to the "real" units?

Any help is appreciated,
-Jill
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