[yt-users] projection results

Sam Skillman samskillman at gmail.com
Mon Jun 11 13:32:00 PDT 2012


Geoffrey, if it helps, in the continuum limit, a weighted projection along
the z direction is (v is the field, w is the weight):
[image: Inline image 1]
whereas unweighted is:
[image: Inline image 4]
For your example, the order of magnitude of your result would be
O(density)**2*O(L)/O(density)*O(L) = O(density) for the weighted
projection.  The unweighted is just O(density)*O(L).

Sam

On Mon, Jun 11, 2012 at 2:12 PM, Matthew Turk <matthewturk at gmail.com> wrote:

> Hi Geoffrey,
>
> On Mon, Jun 11, 2012 at 4:10 PM, Geoffrey So <gsiisg at gmail.com> wrote:
> > Hi, sorry for asking a dumb question, but when I do a projection of
> density
> >
> > field = "Density"
> > proj = pf.h.proj(direction, field, weight_field=field)
> >
> > the numbers I get are ~1e-28
> >
> > but when I do
> > proj = pf.h.proj(direction, field, weight_field=None)
> >
> > the numbers become ~1e-4
> >
> > this is a 64 cube simulation, if I were to multiply 64 * 1e-28 for a
> > projection with no weighting, shouldn't I still get numbers on the order
> of
> > 1e-26 or 1e-27?  I'm guessing there's something I've misunderstood about
> > pf.h.proj.  Am I missing like a CGS conversion factor when I don't
> weight it
> > by some field?
>
> Nope, weighting means to take the average with respect to some other
> field.  So when you don't weight it, you don't take an average, you
> get a line integral.  It's probably different by a factor of roughly
> the same OOM as the number of centimeters your box is across.
>
> -Matt
>
> >
> > From
> > G.S.
> >
> > _______________________________________________
> > yt-users mailing list
> > yt-users at lists.spacepope.org
> > http://lists.spacepope.org/listinfo.cgi/yt-users-spacepope.org
> >
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