Returns the hyperbolic arc tangent of its argument.

    This function is supported on OpenVMS Integrity servers and
    Alpha only.

    Format

      #include  <math.h>

      double atanh  (double x);

      float atanhf  (float x);

      long double atanhl  (long double x);

1 - Argument

 x

    A radian expressed as a real value in the domain [-1,1].

2 - Description

    The atanh functions return the hyperbolic arc tangent of x.
    The atanh function is the inverse function of tanh where
    atanh(tanh(x)) = x.

    |x| > 1 is an invalid argument.