ATANH(3P)                                           POSIX Programmer's Manual                                          ATANH(3P)



PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (con-
       sult the corresponding Linux manual page for details of Linux behavior), or the  interface  may  not  be  implemented  on
       Linux.

NAME
       atanh, atanhf, atanhl - inverse hyperbolic tangent functions

SYNOPSIS
       #include <math.h>

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


DESCRIPTION
       These functions shall compute the inverse hyperbolic tangent of their argument x.

       An  application  wishing  to  check  for  error situations should set errno to zero and call feclearexcept(FE_ALL_EXCEPT)
       before calling these functions.  On return, if errno is non-zero or fetestexcept(FE_INVALID | FE_DIVBYZERO |  FE_OVERFLOW
       | FE_UNDERFLOW) is non-zero, an error has occurred.

RETURN VALUE
       Upon successful completion, these functions shall return the inverse hyperbolic tangent of their argument.

       If  x is +-1, a pole error shall occur, and atanh(), atanhf(), and atanhl() shall return the value of the macro HUGE_VAL,
       HUGE_VALF, and HUGE_VALL, respectively, with the same sign as the correct value of the function.

       For finite |x|>1, a domain error shall occur, and  either a NaN (if supported), or an implementation-defined value  shall
       be returned.

       If x is NaN, a NaN shall be returned.

       If x is +-0, x shall be returned.

       If  x  is +-Inf, a domain error shall occur, and either a NaN (if supported), or an implementation-defined value shall be
       returned.

       If x is subnormal, a range error may occur and x should be returned.

ERRORS
       These functions shall fail if:

       Domain Error
              The x argument is finite and not in the range [-1,1],  or is +-Inf.

       If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [EDOM]. If the  integer
       expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception shall be raised.

       Pole Error
              The x argument is +-1.

       If  the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [ERANGE]. If the inte-
       ger expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the divide-by-zero floating-point exception shall be
       raised.



       These functions may fail if:

       Range Error
              The value of x is subnormal.

       If  the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [ERANGE]. If the inte-
       ger expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the  underflow  floating-point  exception  shall  be
       raised.


       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       On error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling & MATH_ERREXCEPT) are independent of each
       other, but at least one of them must be non-zero.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       feclearexcept(), fetestexcept(), tanh(), the Base Definitions volume of IEEE Std 1003.1-2001, Section 4.18, Treatment  of
       Error Conditions for Mathematical Functions, <math.h>

COPYRIGHT
       Portions  of  this  text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for
       Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6,  Copy-
       right (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any
       discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open  Group
       Standard   is   the   referee   document.   The   original   Standard   can   be   obtained  online  at  http://www.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                     ATANH(3P)