Hi Nathan, I would just like to add that once you get this working, a field like this seems like it would be useful to a number of people. If you're up for it, I would encourage you to submit a yt script with just the definition of the field to the yt hub. Perhaps we should even have a section devoted complex field definitions. Britton On Wed, Sep 7, 2011 at 3:55 AM, Matthew Turk <matthewturk@gmail.com> wrote:
Hi Nathan,
On Wed, Sep 7, 2011 at 3:30 AM, Nathan Goldbaum <goldbaum@ucolick.org> wrote:
Hi Andrew, Thanks for the idea. Unfortunately, that doesn't seem to be the problem. I just tried taking the absolute value of R cross V before taking the square root and got the exact same results.
Your script actually did not work for me on a standard AMR dataset. The axes of the result of the cross product were transposed from what they should be; my script died on a grid of size (18, 16, 16) because the result of the cross product was (16, 16, 18) and the CylinderRadius variable was (18, 16, 16). Naively applying a transpose (although I am not sure why I had to do this) and Andrew's suggestion of na.abs produced plots that looked vaguely correct. I recognize this is perhaps not a satisfying answer, but I would encourage you to investigate how the axes in the na.cross function are modified and returned; I also noted that only specifying "axis=0" instead of "axisa=0" and "axisb=0" got me the same result. I suspect that not specifying "axisc=0" is the cause of the problem. Another note is that I end up with a singularity at the y=z line.
If you end up wanting to do this *not* aligned with the axes, the off-axis projection method will probably be of some help. It would be very nice if we had some kind of recipe or script for calculating Toomre Q; I have done it myself, but unfortunately the script I used to calculate it was not backed up and was wiped out in a colossal and deep-cutting hard drive failure at SDSC, and so I am unable to share it.
Best,
Matt
-Nathan On Sep 6, 2011, at 11:43 PM, Andrew Myers wrote:
Hi Nathan,
This is just a guess, but do you really mean to be taking the square root of R cross V, at line 30? That quantity could potentially be negative, depending on the sense in which the fluid is spinning.
-Andrew Myers
On Tue, Sep 6, 2011 at 5:54 PM, Nathan Goldbaum <goldbaum@ucolick.org> wrote:
Hello all, Right now I'm trying to generate maps of the Toomre Q in an isolated galaxy simulation. To do so, I'm using yt to generate maps of the gas column density as well as density-weighted projections of the sound
and orbital frequency, which I'm using as a proxy for the epicyclic frequency. Unfortunately, I'm having some trouble making projected maps of the orbital frequency. I've defined two new derived fields, CylinderRadius and AngularVelocity (http://paste.yt-project.org/show/1784/). When I try to project the AngularVelocity field, I get what looks like garbage: http://i.imgur.com/PkYhe.png However, slices work just fine: http://i.imgur.com/NnEbq.png I've written the derived fields in a coordinate-dependent way, since I'll always be doing projections down a fixed axis. Is that where my problem lies? My understanding of how yt does projections is too shallow to
speed figure
out exactly what's going wrong here, so I'm hoping the collective wisdom of the yt developers and user base can come to the rescue. Best regards, Nathan Goldbaum Graduate Student Astronomy & Astrophysics, UCSC goldbaum@ucolick.org http://www.ucolick.org/~goldbaum
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