ATANH(3)		   Linux Programmer's Manual		      ATANH(3)



NAME
       atanh, atanhf, atanhl - inverse hyperbolic tangent function

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():
	   _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
	       || _XOPEN_SOURCE >= 500
	       || /* Since glibc 2.19: */ _DEFAULT_SOURCE
	       || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

       atanhf(), atanhl():
	   _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
	       || /* Since glibc 2.19: */ _DEFAULT_SOURCE
	       || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION
       These  functions calculate 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.

ATTRIBUTES
       For  an	explanation  of	 the  terms  used   in	 this	section,   see
       attributes(7).

       +-----------------------------+---------------+---------+
       |Interface		     | Attribute     | Value   |
       +-----------------------------+---------------+---------+
       |atanh(), atanhf(), atanhl()  | Thread safety | MT-Safe |
       +-----------------------------+---------------+---------+
CONFORMING TO
       C99, POSIX.1-2001, POSIX.1-2008.

       The variant returning double also conforms to SVr4, 4.3BSD, C89.

BUGS
       In  glibc  2.9  and  earlier, when a pole error occurs, errno as set to
       EDOM instead of the POSIX-mandated ERANGE.  Since version  2.10,	 glibc
       does the right thing.

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

COLOPHON
       This  page  is  part of release 4.10 of the Linux man-pages project.  A
       description of the project, information about reporting bugs,  and  the
       latest	  version     of     this    page,    can    be	   found    at
       https://www.kernel.org/doc/man-pages/.



				  2016-03-15			      ATANH(3)