[yt-users] Velocity dispersion profile

John ZuHone jzuhone at head.cfa.harvard.edu
Wed Feb 29 13:11:06 PST 2012


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 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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