[yt-users] Light Cone Projection

[Britton Smith]

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 at 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 at 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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>>
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