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():
           _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED ||
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
           or cc -std=c99
       atanhf(), atanhl():
           _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
           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 mathematically 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 floating-point exception (FE_DIVBYZERO)
              is raised.

CONFORMING TO

       C99, POSIX.1-2001.  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 3.54 of the Linux man-pages project.  A description of the project, and
       information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.

                                                   2010-09-11                                           ATANH(3)