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