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 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.

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.

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  5.10  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/.

                                                   2017-09-15                                           ATANH(3)