NAME

       atanh, atanhf, atanhl - inverse hyperbolic tangent function

LIBRARY

       Math library (libm, -lm)

SYNOPSIS

       #include <math.h>

       double atanh(double x);
       float atanhf(float x);
       long double atanhl(long double x);

   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 <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

       atanhf(), atanhl():
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* glibc <= 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 │
       └───────────────────────────────────────────────────────────────┴───────────────┴─────────┘

STANDARDS

       C11, POSIX.1-2008.

HISTORY

       C99, POSIX.1-2001.

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

BUGS

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

SEE ALSO

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