#8532: Hyperbolic arc cosine fails on (-1) :: Complex r. -------------------------------------+------------------------------------- Reporter: leftaroundabout | Owner: Type: bug | Status: new Priority: low | Milestone: Component: libraries/base | Version: 7.6.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Unknown/Multiple Type of failure: Incorrect result | Difficulty: Easy (less than 1 at runtime | hour) Test Case: acosh(-1) :: | Blocked By: Complex Double | Related Tickets: Blocking: | -------------------------------------+------------------------------------- Comment (by ekmett): We do pick the standard branch cut location. That said, it is possible to give a more general form with a specified branch cut. I do so for all of these functions and more for quaternions in http://hackage.haskell.org/package/linear-1.10.1.1/docs/Linear- Quaternion.html You pick the location of the branch cut by supplying a unit quaternion. Adapting this logic to a choice of point on the unit circle could be done, but I confess I'd rather hash that out in libraries before asserting it is the right approach for something like base. Almost nobody knows how to use the more exotic cuts, but importantly they can be formed from the standard cut and identities by somone with sufficient background to be aware of the issue. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8532#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler