2015 008 Additional math functions

Proposal 2015-008

Author: Andreas Rossberg
Last revised: August 16, 2015
Status: proposed
Discussion: issue #9

signature MATH =
  sig
    ...
    val asinh : real -> real
    val acosh : real -> real
    val atanh : real -> real
  end

structure Math : MATH

asinh x
returns the arc hyperbolic sine of x, expressed in radians. It is the inverse of the sinh function.
acosh x
returns the nonnegative arc hyperbolic cosine of x, expressed in radians. It is the inverse of the cosh function. If x is less than 0, then the Domain exception is raised.
atanh x
returns the arc hyperbolic tangent of x, expressed in radians. It is the inverse of the tanh function. The Domain exception is raised if x is less than ~1.0 or greater than 1.0.

These are fairly standard in contemporary language's math libraries.

The addition of these functions should not affect existing programs.

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