On Wed, Feb 29, 2012 at 4:16 PM, John Wise <
jwise@physics.gatech.edu> wrote:
> Hi all,
>
> I did something like this a couple of weeks ago, where I did something
> similar to Matt's description. I ripped the relevant part of my script and
> posted it here.
>
>
http://paste.yt-project.org/show/2201/
>
> John
>
>
> On 02/29/2012 04:14 PM, Matthew Turk wrote:
>>
>> Yes, adding a direct stddev would be nice (and would not be too much
>> overhead) but I think this can be done in two passes.
>>
>> Pass one: calculate the average value. This would be a standard profile.
>> Pass two: set_field_parameter of the average value as a function of
>> whatever. Inside your new derived field, calculate the delta between
>> the average and the actual field value. Take average of this new
>> derived field.
>>
>> It's probably a better idea to just add stddev directly. There is an
>> extant algorithm for doing a one-pass stddev that is robust against
>> round-off errors; I would be happy to help someone out to add that to
>> the code.
>>
>> -Matt
>>
>> On Wed, Feb 29, 2012 at 4:11 PM, John ZuHone
>> <
jzuhone@head.cfa.harvard.edu> wrote:
>>>
>>> I do not believe this can be done with the current code. It's something
>>> I'd like to see, however.
>>>
>>> I would be willing to code this up, but it will probably be weeks before
>>> I
>>> have time.
>>>
>>> John Z
>>>
>>> On Wed, 29 Feb 2012, Britton Smith wrote:
>>>
>>>> I think what Junhwan is asking is whether it's possible to do a profile
>>>> of
>>>> velocity dispersion. If I understand correctly, the problem is that
>>>> this
>>>> would require, for every spherical shell in a radial profile, the
>>>> calculation of the standard deviation of the VelocityMagnitude field.
>>>> I'm
>>>> not sure if this is possible within the existing profile framework. Can
>>>> anyone else comment on this?
>>>>
>>>> On Wed, Feb 29, 2012 at 2:25 PM, Nathan
>>>> Goldbaum<
goldbaum@ucolick.org>wrote:
>>>>
>>>>> Hi Junhwan,
>>>>>
>>>>> Can you paste a script and a traceback that shows the error you're
>>>>> seeing?
>>>>> You should be able to pass the BulkVelocity to the derived field via
>>>>> set_field_parameters.
>>>>>
>>>>> You can paste a script from the command line with the following
>>>>> command:
>>>>>
>>>>> yt pastebin name_of_script.py
>>>>>
>>>>> Nathan Goldbaum
>>>>> Graduate Student
>>>>> Astronomy& Astrophysics, UCSC
>>>>>
>>>>>
goldbaum@ucolick.org
>>>>>
http://www.ucolick.org/~goldbaum
>>>>>
>>>>> On Feb 29, 2012, at 8:31 AM, Jun-Hwan Choi wrote:
>>>>>
>>>>> Hi YT users,
>>>>>
>>>>> I would like to make a (spherical and/or cylindrical) profile of the
>>>>> velocity dispersion.
>>>>> In order to do so, I need to compute the mean velocity (BulkVelocity)
>>>>> for
>>>>> a given shell (or ring), and pass this value to newly defined velocity
>>>>> dispersion field, and then make a profile for the velocity dispersion
>>>>> field.
>>>>> Is there a particular way in yt to handle this?
>>>>>
>>>>> Junhwan
>>>>>
>>>>> P.S.: A few weeks ago I posted a similar question and Matt gave me a
>>>>> following hint.
>>>>> @derived_field(name = "deltaLocalCircularVelocity")
>>>>> def delta_LocalCircularVelocity(fi
>>>>> eld, data):
>>>>> fn, x, cv = data.get_field_parameter("local_circular_velocity")
>>>>> cv0 = na.interp(data[fn].ravel(), x, cv)
>>>>> cv0 = cv0.reshape(data[fn].shape)
>>>>> delta_cv = cv0 - data["LocalCircularVelocity"]
>>>>> return delta_cv
>>>>>
>>>>> You'll need to do something like this on the data object from which
>>>>> you are getting your data:
>>>>>
>>>>> sp.set_field_parameter("local_circular_velocity",
>>>>> (fn, prof[fn], prof["LocalCircularVelocity"]))
>>>>>
>>>>> However, it does not work for me and it is also complicate to
>>>>> understand
>>>>> and modify it.
>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> --------------------------------------------------------------
>>>>> Jun-Hwan Choi, Ph.D.
>>>>> Department of Physics and Astronomy, University of Kentucky
>>>>> Tel:
(859) 897-6737 Fax:
(859) 323-2846
>>>>> Email:
jhchoi@pa.uky.edu URL:
http://www.pa.uky.edu/~jhchoi
>>>>> --------------------------------------------------------------
>>>>>
>>>>>
>>>>> !DSPAM:10175,4f4e76d329502195409319!
>>>>> _______________________________________________
>>>>>
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>>>>>
>>>>>
>>>>>
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>
>
> --
> John Wise
> Assistant Professor of Physics
> Center for Relativistic Astrophysics, Georgia Tech
>
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