I don't know how often these features get used, but I would vote to not make this a big deal.  I would say include it in the list of bugfixes in the next point release, but it may not necessitate an email to the whole list about the issue.  

Notably, I ran into similar issue last week during some analysis with the cylindrical coordinate system, but I tested it first to see if it made sense.  I anticipate that other users would do the same thing instead of just assuming its all correct, but maybe I'm wrong?  I've been meaning to make a bug report on the cylindrical dataset, but maybe your PR has corrected the issues I encountered.

Thanks for your and Philipp's work to correct these issues!

Cameron

On Thu, Feb 8, 2018 at 12:09 PM, Nathan Goldbaum <nathan12343@gmail.com> wrote:
Hi all,

I'd like to point out a pull request I just made, which fixes a number of fields that have been returning incorrect data. In particular, the definitions of the fields `velocity_spherical_theta`, `velocity_spherical_phi`, and `velocity_cylindrical_theta` have not been correct for at least three years, possibly longer - I haven't checked to see if they were ever correct.

Here's a pull request that implements a fix and adds some new tests:

https://github.com/yt-project/yt/pull/1687

While it's nice that we know there's an issue now and that it's fixed, this means that if someone was making a profile of the tangential velocity around a star, or the poloidal magnetic field in a disk simulation, or a circular velocity in a galaxy simulation, yt may have silently returned incorrect results.

I'm raising this issue here because it feels like it might be a big deal. Should this concern be raised more loudly to our users? I'm hesitant to do so, mostly out of sheepishness. Is this as big a deal as I'm making it out to be?

Thanks,

Nathan

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--
Cameron Hummels
NSF Postdoctoral Fellow
Department of Astronomy
California Institute of Technology
http://chummels.org