[yt-users] Velocity dispersion profile

[Britton Smith]

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 at 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 at 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 at pa.uky.edu   URL: http://www.pa.uky.edu/~jhchoi
> --------------------------------------------------------------
>
>
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