[GHC] #8532: Hyperbolic arc cosine fails on (-1) :: Complex r.

[GHC]

#8532: Hyperbolic arc cosine fails on (-1) :: Complex r.
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        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:                    |
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Changes (by carter):

 * cc: hvr, ekmett (added)


Comment:

 hrmm, so one issue with complex functions in general is that there (is
 always) a "branch cut"

 http://mathworld.wolfram.com/BranchCut.html

 http://en.wikipedia.org/wiki/Branch_point

 http://math.stackexchange.com/questions/245579/how-does-a-branch-cut-
 define-a-branch

 are some of the first few decent hits on google for this topic.


 So do we standardize on the "common" branch cut choice? I'm not sure. If
 we don't enrich the complex function apis to be somehow parameterized by
 the branchcut choice, thats probably the "right" thing to do. ("right"
 being of course not quite the right term)

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8532#comment:3>
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