I suspect that any user who is doing analysis right now using these fields might want to know right now about this bug so that they can apply the fix immediately if they so desire before they publish something on them. 

In fact, my student is working on a project using these very fields and I just told him that we’ll need to do that very thing—apply this fix and he’ll have to re-run stuff (not a big deal). 

So for that reason we should email yt-users. It’s embarrassing but let’s be honest—we’re not perfect, and even if some people are cranky with us I think that it’s good practice to be very open about these things because I think our users would appreciate it.  

On Feb 8, 2018, at 3:09 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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