atanhl

       #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
       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

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 4.04 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
       http://www.kernel.org/doc/man-pages/.

                                  2015-04-19                          ATANH(3)
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