Re: [yt-users] Velocity dispersion profile

1 Mar 2012


      Ok, I'm in for this.  Let's try meeting on Friday on IRC for some TCB.

Britton

On Wed, Feb 29, 2012 at 4:22 PM, Matthew Turk  wrote:
...
Thanks, John!
And Britton & John ZH, I'd be up for working on this tomorrow or
Friday.  Here's the paper with the one-pass stddev.
http://www.cs.berkeley.edu/~mhoemmen/cs194/Tutorials/variance.pdf
(Formula 5)
Meet up in IRC sometime soon, and try to knock it out?  I think it
would be best if we just always calculated this and stick it in the
profile.  We can calculate it along with the weight.
-Matt
...
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
...
...
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
  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
On Wed, Feb 29, 2012 at 4:16 PM, John Wise 
wrote:
profile.
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
Goldbaumwrote:
...
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!
_______________________________________________
yt-users mailing list
yt-users@lists.spacepope.org
http://lists.spacepope.org/listinfo.cgi/yt-users-spacepope.org
!DSPAM:10175,4f4e76d329502195409319!
_______________________________________________
yt-users mailing list
yt-users@lists.spacepope.org
http://lists.spacepope.org/listinfo.cgi/yt-users-spacepope.org
_______________________________________________
yt-users mailing list
yt-users@lists.spacepope.org
http://lists.spacepope.org/listinfo.cgi/yt-users-spacepope.org
_______________________________________________
yt-users mailing list
yt-users@lists.spacepope.org
http://lists.spacepope.org/listinfo.cgi/yt-users-spacepope.org
--
John Wise
Assistant Professor of Physics
Center for Relativistic Astrophysics, Georgia Tech
_______________________________________________
yt-users mailing list
yt-users@lists.spacepope.org
http://lists.spacepope.org/listinfo.cgi/yt-users-spacepope.org

yt-users mailing list
yt-users@lists.spacepope.org
http://lists.spacepope.org/listinfo.cgi/yt-users-spacepope.org