[yt-users] TotalQuantity vs. summing manually

Geoffrey So gsiisg at gmail.com
Fri Dec 20 18:36:37 PST 2013


So in that case, would using TotalQuantity to sum up particle information
inside 3D container be a bad practice?

From
G.S.


On Fri, Dec 20, 2013 at 6:20 PM, John ZuHone <jzuhone at gmail.com> wrote:

> Geoffrey,
>
> It seems that what is going on here is that whereas the particles in the
> container are simply the ones contained within the container's cells, the
> dark matter density is smeared onto the grid using the cloud-in-cell
> algorithm, meaning that for particles on the edge of their container some
> of their mass has been smeared onto cells just on the outside, which is a
> thing that Enzo does.
>
> So it's not really an apples-to-apples comparison.
>
> John ZuHone
> Laboratory for High-Energy Astrophysics
> NASA/Goddard Space Flight Center
> 8800 Greenbelt Rd., Mail Code 662
> Greenbelt, MD 20771
> (w) 301-286-2531
> (m) 781-708-5004
> john.zuhone at nasa.gov
> jzuhone at gmail.com
>
> > On Dec 20, 2013, at 9:02 PM, Geoffrey So <gsiisg at gmail.com> wrote:
> >
> > Hi all,
> >
> > I found that using a Enzo dataset I was getting slightly different
> numbers when
> > 1) using the list of dark matter particles selected by creation_time <
> 0.0
> >
> > In [97]: sph_dm = sph['creation_time'] < 0.0
> > In [98]: print "%12.12e" % (sph['ParticleMassMsun'][sph_dm]).sum()
> > 1.211311468567e+11
> >
> > 2) compared to summing the dark matter particles inside a 3D container
> with TotalQuantity
> >
> > In [101]: print "%12.12e" %
> (sph.quantities['TotalQuantity']('Dark_Matter_Density')[0]*vol/Msun)
> > 1.188937185993e+11
> >
> > I'm wondering if the field and particles are handled differently when
> being counted as inside or outside the 3D container?
> >
> > From
> > G.S.
> > _______________________________________________
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