Hi Josh,

I think I was able to find the source of the error.  There was a case in which rays start on the edge of the domain and are oriented outward that I hadn't accounted for correctly.  I've just pushed a fix for this to the development branch of yt.  If you update to the yt branch within the repo, it should be fine.  However, there was also a minor change in the LightRay api, so you'll need to adjust your script a little bit.  If you change your script to resemble something like the following:
http://paste.yt-project.org/show/2579/
everything should be fine.

Let me know if you encounter any more issues.

Britton

On Fri, Jul 27, 2012 at 7:18 PM, Britton Smith <brittonsmith@gmail.com> wrote:

Hi Josh,

I'm not sure what's causing that as it's never happened to me before. I'm away from my computer at the moment but I will take a look at this later. Is the script you're using unaltered?  If not, please send me the one you're using off-list.

Also, please make sure to send emails to the list from the address that you signed up with. Otherwise, it has to be approved by the moderator each time.

Britton

On Jul 27, 2012 7:05 PM, "Joshua Eric Moloney" <Joshua.Moloney@colorado.edu> wrote:
The install I'm running should be the latest stable version of the code:

The current version of the code is:

---
c23cb264f04c (stable)
---

-Josh


On Fri, Jul 27, 2012 at 4:54 PM, Nathan Goldbaum <nathan12343@gmail.com> wrote:
Hi Joshua,

I can't speak to the problem you're having specifically.  However, since there have been some recent updates to the light ray, it would help us to figure out what's happening if you could reply with the output of the "yt instinfo" command, run on the command line.

Cheers,

Nathan

On Jul 27, 2012, at 3:49 PM, Joshua Eric Moloney wrote:

Hi all,

I've been trying to get a script (provided to me by Britton) working to create a bunch of light rays from an Enzo simulation. Depending on the initial seed value, it makes some of them correctly but eventually fails with the following error:

Traceback (most recent call last):
  File "make_light_rays.py", line 32, in <module>
    get_los_velocity=True, get_nearest_galaxy=False)
  File "/home/student/jomo9722/Enzo/
yt-x86_64/src/yt-hg/yt/analysis_modules/light_ray/light_ray.py", line 275, in make_light_ray
    (sub_ray[field])])
  File "/home/student/jomo9722/Enzo/yt-x86_64/src/yt-hg/yt/data_objects/data_containers.py", line 319, in __getitem__
    self.get_data(key)
  File "/home/student/jomo9722/Enzo/yt-x86_64/src/yt-hg/yt/data_objects/data_containers.py", line 508, in get_data
    if field not in ("dts", "t") and self._generate_field(field):
  File "/home/student/jomo9722/Enzo/yt-x86_64/src/yt-hg/yt/data_objects/data_containers.py", line 349, in _generate_field
    self[field] = self.pf.field_info[field](self)
  File "/home/student/jomo9722/Enzo/yt-x86_64/src/yt-hg/yt/data_objects/field_info_container.py", line 316, in __call__
    dd = self._function(self, data)
  File "/data/moloney/cosmology_test/test_new/ion_balance/SD93IonBalance.py", line 178, in _ion_number_density
    return solarAbundance[atom] * data[fractionField] * data['Metallicity'] * \
  File "/home/student/jomo9722/Enzo/yt-x86_64/src/yt-hg/yt/data_objects/data_containers.py", line 319, in __getitem__
    self.get_data(key)
  File "/home/student/jomo9722/Enzo/yt-x86_64/src/yt-hg/yt/data_objects/data_containers.py", line 508, in get_data
    if field not in ("dts", "t") and self._generate_field(field):
  File "/home/student/jomo9722/Enzo/yt-x86_64/src/yt-hg/yt/data_objects/data_containers.py", line 349, in _generate_field
    self[field] = self.pf.field_info[field](self)
  File "/home/student/jomo9722/Enzo/yt-x86_64/src/yt-hg/yt/data_objects/field_info_container.py", line 316, in __call__
    dd = self._function(self, data)
  File "/data/moloney/cosmology_test/test_new/ion_balance/SD93IonBalance.py", line 193, in _ion_fraction_field
    fraction = na.power(10, interp(data))
  File "/home/student/jomo9722/Enzo/yt-x86_64/src/yt-hg/yt/utilities/linear_interpolators.py", line 44, in __call__
    x_i = (na.digitize(x_vals, self.x_bins) - 1).astype('int32')
ValueError: Both x and bins must have non-zero length

Working through the debugger, I found that for the segment where it failed the periodic_ray function had produced the following list of segments.

[[array([ 0.16103374,  0.78830872,  0.24846128]), array([ 0.14031834,  0.57367409,  1.        ])], [array([ 0.14031834,  0.57367409,  1.        ]), array([ 0.14031834,  0.57367409,  1.        ])], [array([ 0.14031834,  0.57367409,  0.        ]), array([ 0.13268221,  0.49455532,  0.2770327 ])]]

The second segment here has identical start and end points, which is leading yt to try to interpolate a field with nothing in it (and therefore throwing the above error). It seems that what's happening is that due to rounding errors the first segment being produced actually has a value < 1 for the third dimension so that when it checks to see if the segment hit any of the box walls it thinks that it didn't. It then tries to start a new segment that's already at the boundary of the box, producing a ray segment containing 0 grid cells.

Has anyone run into this problem before, and is there a fix for it floating around out there somewhere? If not I could probably work something up that checks to see if the distance from the segment endpoint to the wall is < SmallNumber and set it equal to the value at the wall if it is.

Thanks.
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