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)