Why is the Quaternion logarithmic map given a private-looking name?

[jpreiss]

Why is Quaternion._ln not given a name like Quaternion.log and documented as part of the public interface?

This was asked a while back, but it was tangential to the main topic and thus ignored:

BTW, Is it any reason to avoid conventional log name for method. There is only _ln. Leading underscore in the method name may confuse since it looks like a private method. Maybe, adding log = _ln to the class definition makes sense.

Originally posted by @vr050714 in #21576 (comment)

It seems odd to me, especially since Quaternion.exp is public. There are many use cases of quaternions where we wish to go between the Lie group and Lie algebra in both directions.

[oscarbenjamin]

I think it could be made a public method. I'm not sure if more tidying up or something is needed.

[jpreiss]

I can make a PR if desired!

[oscarbenjamin]

Yes, go ahead.