This is maybe a bit tangential (oh boy, that pun wasn’t intended), but I’m looking for some sort of article that discusses the tangent half-angle link function (tan-half) used in brms as the default link for von Mises distributions. In all my searching online I have found exactly one bit of documentation (from the R package circtree) that explains that the link is used to restrict values to the (-\pi, +\pi) range. Are there any other articles (or brms documentation) further discussing this? I’d like to understand how/why this is implemented, why it’s the default link, etc.

Thanks!