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       atanh, atanhf, atanhl - inverse hyperbolic tangent function


       #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


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


       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
       mathematically correct sign.

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


       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
              floating-point exception (FE_DIVBYZERO) is raised.


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


       For a pole error, errno is set to EDOM; POSIX.1 says it should  be  set
       to ERANGE.


       acosh(3), asinh(3), catanh(3), cosh(3), sinh(3), tanh(3)


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