[yt-dev] Issue #969: Metallicity values reported by LightRay in 3.0 significantly differ from metallicity values in 2.x (yt_analysis/yt)

[Cameron Hummels]

New issue 969: Metallicity values reported by LightRay in 3.0 significantly differ from metallicity values in 2.x
https://bitbucket.org/yt_analysis/yt/issue/969/metallicity-values-reported-by-lightray-in

Cameron Hummels:

I've run into an insidious bug in the LightRay analysis module, wherein metallicity values reported along the light ray in yt 3.0 differ by an OOM with metallicity values reported along the light ray in 2.x.  Strangely enough, temperature values between the two versions don't change at all, and density values only change at the <1e-4 level.  

I have investigated this to some degree and it appears that the bug is confined to the LightRay analysis module, as I'm seeing the same metallicity values for raw ``Ray`` and other data objects between the two versions of yt.

The following scripts demonstrate this problem with the enzo_cosmology_plus dataset.  Because of the way in which the LightRay object operates, you'll need to run these scripts *inside* the enzo_cosmology_plus directory.

For yt-2.x, run this script in the enzo_cosmology_plus directory:
http://paste.yt-project.org/show/5323/

With the resulting output:

```
#!python

Density: [  9.97279296e-32   9.20237619e-31]
Temperature: [  1706.254685    75236.83753987]
Metallicity: [  4.96203366e-09   4.62205944e-09]
```


For yt-3.0, run this script in the enzo_cosmology_plus directory:
http://paste.yt-project.org/show/5324/

With the resulting output:

```
#!python

Density: [  9.97278399e-32   9.20236791e-31]     
Temperature: [  1706.254685    75236.83753987] 
Metallicity: [  1.01225503e-10   9.42900276e-11]
```