Computation of mean, median, and mode of a set of rotations (quaternions). Mean and median functions are PyTorch implementations of algorithms in http://tbirdal.blogspot.com/2019/10/i-allocate-this-post-to-providing.html.

References:

• Markley, F. Landis, et al. "Averaging quaternions." Journal of Guidance, Control, and Dynamics 30.4 (2007): 1193-1197.
• Aftab, Khurrum, Richard Hartley, and Jochen Trumpf. "Generalized weiszfeld algorithms for lq optimization." IEEE transactions on pattern analysis and machine intelligence 37.4 (2014): 728-745.
• https://en.wikipedia.org/wiki/Mode_(statistics)#Mode_of_a_sample