Hi all, 

So I think I found a bug in cut_region.  Right now the directions say you can chain cut regions in two ways:  either listing several cut_regions or using one call and an "&".
http://yt-project.org/doc/analyzing/filtering.html
However, for some extremely mysterious reason, when I do a multi-call to cut_region I get wackadoo numbers, like too high by a couple orders of magnitude.  

Here is the quick check that should work on IsoGal:

ds = yt.load("/data001/stonnes/BPr16vs30arcfo/DD"+loop[i]+"/BPr16vs30arcfo"+loop[i])
    
    disk3 = ds.disk([0.5,0.5,0.5],[0,0,-1.0],(40,"kpc"),(10,"kpc"))
    
    diskn = disk3.cut_region(["obj['Metal_Density']/obj['density'] > 0.5"])
    diska = diskn.cut_region(["obj['density'] > 1e-25"])
    diskd = disk3.cut_region(["(obj['Metal_Density']/obj['density'] > 0.5) & (obj['density'] > 1e-25)"])
    
    print diska.quantities.total_quantity([("gas","cell_mass")])
    print disk3.quantities.total_quantity([("gas","cell_mass")])
    print diskn.quantities.total_quantity([("gas","cell_mass")])
    print diskd.quantities.total_quantity([("gas","cell_mass")])

I am also attaching my whole code, which is a loop, just in case.  So here the diska mass is two orders of magnitude larger than any of the others, and diskd is what I would expect with the two selection criteria.

Best,
Stephanie
--
Dr. Stephanie Tonnesen
Alvin E. Nashman Postdoctoral Fellow
Carnegie Observatories, Pasadena, CA
stonnes@gmail.com