Hi Pengfei,

Thank you for catching all of those errors in the source and documentation.  As of now, they have all been fixed and if you do "yt update" the recipe should run as normal without the need to alter anything.

I can answer your additional questions here.

(1) What's the initial spectrum before any absorption? 

The spectrum generator only creates absorption features.  Essentially, it assumes that you have already subtracted off the continuum, so effectively the input spectrum is just f(lambda) = 1.0.
 
(2) Where does the light ray originate from? Is it shoot from a random position in the first dataset? Can we set it manually like on the surface of the box? Does it go out of the box and back into it until the next output redshift?

The light ray originates in a random position inside the first dataset with a random trajectory.  This code assumes a periodic domain, so the ray will wrap around if it leaves the box.  Once it has traversed a distance equivalent to the comoving distance to the next dataset, it terminates and begins a new ray there.  Currently, you can not manually set the initial position of a LightRay, but you can also using the ray object (http://yt-project.org/doc/analyzing/objects.html#available-objects).  If you are interested in adding support to the LightRay object for setting a fixed initial position (and presumably a fixed end position), let me know and I can help you get started.  If you were to do this, we would be very pleased do have you contribute this code back to the main code base.
 
(3) In the output file lightraysolution.txt, what do the parameters(dl/box, Start x/y/z, End x/y/z) mean?

Since the start and stop positions are randomly chosen, this file shows what those random positions are for each dataset, in case you want to know that.  dl/box is the fraction of the box length that was used for a ray in that dataset.  For more information on this, I would suggest you check out this page:
http://yt-project.org/doc/analysis_modules/light_ray_generator.html#light-ray-generator

Britton
 

Sorry that I have so many questions... I wonder if there is some existing documents or paper that have a more detailed description. 

Thank you again for your help! Have a nice weekend!

Pengfei



2013/9/6 Britton Smith <brittonsmith@gmail.com>
Hi Pengfei,

The near_redshift and far_redshift are free parameters for you to set, and just control the redshift interval over which to make the light cone projection.  You might also want to look at the narrative documentation on the light cone generator, which you can find here:
http://yt-project.org/doc/analysis_modules/light_cone_generator.html
Note, that you need to use this with a simulation that made enough data outputs to connect the redshift interval you specify.  The "enzo_tiny_cosmology" dataset available at http://yt-project.org/data/ was configured to work with the light cone recipe in the cookbook, so I would suggest downloading that.

As for the error, this is happening because there is a line in your enzo parameter file that contains more than one "=" sign.  I have just submitted a pull request that fixes it, so this should be fixed soon.  In the mean time, you can simply comment out that line in your parameter file and everything should work fine.

Britton


On Fri, Sep 6, 2013 at 3:02 AM, Pengfei Chen <madcpf@gmail.com> wrote:
Hi all,

I downloaded the example script of light cone projectoin(http://yt-project.org/doc/cookbook/cosmological_analysis.html#light-cone-projection) to my laptop and changed the Enzo simulation parameter file and redshifts. But when I ran it the following error occurred:

  File "light_cone_projection.py", line 19, in <module>
    find_outputs=False)
  File "/Users/madcpf/Documents/dev_yt/src/yt-hg/yt/analysis_modules/cosmological_observation/light_cone/light_cone.py", line 158, in __init__
    find_outputs=find_outputs)
  File "/Users/madcpf/Documents/dev_yt/src/yt-hg/yt/analysis_modules/cosmological_observation/cosmology_splice.py", line 44, in __init__
    find_outputs=find_outputs)
  File "/Users/madcpf/Documents/dev_yt/src/yt-hg/yt/convenience.py", line 131, in simulation
    find_outputs=find_outputs)
  File "/Users/madcpf/Documents/dev_yt/src/yt-hg/yt/frontends/enzo/simulation_handling.py", line 81, in __init__
    find_outputs=find_outputs)
  File "/Users/madcpf/Documents/dev_yt/src/yt-hg/yt/data_objects/time_series.py", line 343, in __init__
    self._parse_parameter_file()
  File "/Users/madcpf/Documents/dev_yt/src/yt-hg/yt/frontends/enzo/simulation_handling.py", line 273, in _parse_parameter_file
    param, vals = (i.strip() for i in line.split("="))
ValueError: need more than 1 value to unpack

Does the parameters "near_redshift" and "far_redshift" in LightCone need to be the same with "CosmologyFinalRedshift" and "CosmologyInitialRedshift" in enzo parameter file?
Does anyone know how to solve this?

Thank you all!

Pengfei

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