[yt-users] cut_region bafflement

[Stephanie Tonnesen]

Dear yt-users,

I am running

Version = 3.2-dev
Changeset = dc2467c4eae7 (yt) tip

I have been fiddling around with cut_region in a disk region and have
gotten really confused.  I was initially trying to see whether defining a
disk region such that the cylinder height was on the x-axis changed how I
need to make a cut in the cylinder height.  Anyway, as I was fiddling with
these cuts I found that if I made a "spatial" cut (rather than a different
variable cut) I was getting different volumes.  Let me show you:

small bit of background:  the whole box is 130 kpc across, so 0.5 0.5 0.5
is 65 65 65 kpc.  Also, I am cutting and pasting bits here so the
indentation is off.

ds =
yt.load("/data/stonnes/dwarf_nowind_lowmassgal_bigtracer/DD"+loop[i]+"/DD44sMBhn25now"+loop[i])

r2 = ds.disk([0.5,0.5,0.5],[-1,0,0],(4,"kpc"),(2,"kpc"))
    r2c = r2.cut_region(["obj['Metal_Density']/obj['density'] > 0.33"])

    r3 = ds.disk([0.5,0.5,0.5],[-1,0,0],(4,"kpc"),(2,"kpc"))
    r3r = r3.cut_region(["(obj['x'].in_units('kpc') > 63.0)"])
    r3r = r3r.cut_region(["(obj['x'].in_units('kpc') < 67.0)"])
    r3c = r3r.cut_region(["obj['Metal_Density']/obj['density'] > 0.33"])

    r4 = ds.disk([0.5,0.5,0.5],[-1,0,0],(4,"kpc"),(2,"kpc"))
    r4r = r4.cut_region(["(obj['x'].in_units('kpc') > 61.)"])
    r4c = r4r.cut_region(["obj['Metal_Density']/obj['density'] > 0.33"])

 P2 = np.append(P2,r2c.quantities.total_quantity([("index","cell_volume")]))
 P3 = np.append(P3,r3c.quantities.total_quantity([("index","cell_volume")]))
 P4 = np.append(P4,r4c.quantities.total_quantity([("index","cell_volume")]))

P2 volume is 9.346e-5 : within 2% of my calculation for the volume I should
be getting
P3 volume is 7.4768e-4
P4 volume is 7.4768e-4

When I print out the x- y- and z- maxes and mins, they are the same for
each of the selected regions.
(By doing this:
m2 = np.append(m2,r2c.quantities.extrema([("index","z")])[0])
rho2 = np.append(rho2,r2c.quantities.extrema([("index","z")])[1])

)

Can anyone help me figure out/tell me what is going on here?

Thanks!
Stephanie

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