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       atanh, atanhf, atanhl - inverse hyperbolic tangent function


       #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)):

           _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


       These  functions  calculate  the  inverse hyperbolic tangent of x; that is the value whose
       hyperbolic tangent is x.


       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


       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.


       For an explanation of the terms used in this section, see attributes(7).

       │InterfaceAttributeValue   │
       │atanh(), atanhf(), atanhl()  │ Thread safety │ MT-Safe │


       C99, POSIX.1-2001, POSIX.1-2008.

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


       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.


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


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                                            2017-09-15                                   ATANH(3)