atanh

SYNOPSIS
       #include <math.h>

       double atanh(double x);
       float atanhf(float x);
       long double atanhl(long double x);

       Link with -lm.

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       atanh(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 ||
       _ISOC99_SOURCE; or cc -std=c99
       atanhf(), atanhl(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600
       || _ISOC99_SOURCE; or cc -std=c99

DESCRIPTION
       The  atanh()  function  calculates the inverse hyperbolic tangent of x;
       that is the value whose hyperbolic tangent is x.

RETURN VALUE
       On success, these functions return the inverse hyperbolic tangent of x.

       If x is a NaN, a NaN is returned.

       If x is +0 (-0), +0 (-0) is returned.

       If x is +1 or -1,  a  pole  error  occurs,  and  the  functions  return
       HUGE_VAL,  HUGE_VALF,  or  HUGE_VALL, respectively, with the mathemati-
       cally correct sign.

       If the absolute value of x is greater than 1, a  domain  error  occurs,
       and a NaN is returned.

ERRORS
       See  math_error(7) for information on how to determine whether an error
       has occurred when calling these functions.

       The following errors can occur:

       Domain error: x less than -1 or greater than +1
              errno is set  to  EDOM.   An  invalid  floating-point  exception
              (FE_INVALID) is raised.

       Pole error: x is +1 or -1
              errno  is set to ERANGE (but see BUGS).  A divide-by-zero float-
              ing-point exception (FE_DIVBYZERO) is raised.

CONFORMING TO
       C99, POSIX.1-2001.  The variant returning double also conforms to SVr4,
       4.3BSD, C89.

BUGS

                                  2008-08-05                          ATANH(3)