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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 (consult 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  sup-
       ported), 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  integer  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  integer 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, Copyright (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.opengroup.org/unix/online.html .

IEEE/The Open Group                  2003                            ATANH(3P)