When I run each method over the whole volume, the kd-tree and the HV
take the same duration to process, however, the ratio of the two is
still the same factor of 2e-8.
On 11/22/11 3:26 PM, Sam Skillman wrote:
Are the answers similar if you do the entire volume? The kd-tree can
not accept things like spheres to homogenize over, so maybe it is
because it is projecting the entire box? I'll keep thinking...
On Tue, Nov 22, 2011 at 1:07 PM, Cameron Hummels <chummels(a)gmail.com
Hello peeps (mostly Britton, Matt and Sam),
I have recently been doing some off-axis projections in my
cosmological runs (using the supercool new off_axis_projection
helper function Matt wrote), and I've encountered some problems.
I find different results when I do the off-axis projection using
a homogenized volume versus when I do not use a homogenized volume
(when it uses the default behavior for camera objects -- ie a KDtree).
Of course, these two results should be identical, and they are
when I use a normal field like "Density". However, I'm trying to
use a derived field from some code Britton wrote, part of a
package called ion_balance, which creates derived fields for
different atomic ions. So when I compare the CIV Number Density
from these two methods, I get very different results. Even when I
do this on a normal vanilla yt field, like "Density", the KDtree
method takes exceptionally longer than the homogenized volume
method (I think this is because I'm only doing the HV for a small
subsample of the overall volume). On the other hand, they both
take about the same amount of time when my sample volume is the
entire box volume.
I've pastebinned a demonstration script which shows this
discrepancy at: http://paste.yt-project.org/show/1953
. If you
don't have ion_balance, you can comment that import out, and
comment the line for defining the field as
"CIV_Cloudy_eq_NumberDensity", and run it to see the time
discrepancy between the two methods. It should work on any sort
of parameter file, not just the specific one I'm using. What I do
is take an off-axis projection using each method, then divide the
two images against each other to form a ratio image, and then
output the average and stddev for this ratio. The average of the
ratio is: 2e-8.
I've changed the width of the off-axis projection and it has a
minimal (but nonzero) change on the overall ratio between the two.
So I'm not sure what to do. It appears that the CIV field is
initiated in the same way that a normal field is, with the
projection_conversion set to 'cm', just as it is for "Density".
Any ideas on what could be making this difference? Any ideas on
which is the value to trust?
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