[yt-users] question about derived fields that require field_parameters

[Brian O'Shea]

Hi folks,

I'm doing some analysis on an Enzo simulation using the tip of yt-3, and
would like to find the maximum and minimum of the field
"baryon_overdensity", which is a derived field.  If I were to make a
projection or slice of this field, I'd have to feed in omega_baryon so that
baryon_overdensity can be created on the fly, e.g.,

plot1 =
yt.ProjectionPlot(ds,'z',"baryon_overdensity",weight_field="baryon_overdensity",
                              center=c,data_source=my_region,
field_parameters = {'omega_baryon': 0.046})

However, if I try to run find_max("baryon_overdensity") on my dataset, it
complains that the derived field needs omega_baryon, with an error message
ending in this:

/Users/bwoshea/Desktop/yt-3/src/yt-hg/yt/fields/derived_field.pyc in
__call__(self, data)
    237                 doesnt_have.append(p)
    238         if len(doesnt_have) > 0:
--> 239             raise NeedsParameter(doesnt_have)
    240         return True
    241

NeedsParameter: (['omega_baryon'])


This makes sense; however, I can't feed omega_baryon to find_max() in the
same way that I can feed field_parameters into ProjectionPlot.  Is there a
way to either (1) force yt to generate the baryon_overdensity field prior
to calling find_max(), or (2) feed omega_baryon into find_max()?  I think
that option #2 is not trivial, since the source code for find_max (in
src/yt-hg/yt/data_objects/static_objects.py) only takes the name of the
field.  I suspect that #1 is possible, though I can't find anything in the
documentation about it.

Any suggestions would be greatly appreciated.  Thanks!

--Brian
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