1ATANH(3P)                  POSIX Programmer's Manual                 ATANH(3P)
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PROLOG

6       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
7       implementation of this interface may differ (consult the  corresponding
8       Linux  manual page for details of Linux behavior), or the interface may
9       not be implemented on Linux.
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NAME

12       atanh, atanhf, atanhl - inverse hyperbolic tangent functions
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SYNOPSIS

15       #include <math.h>
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17       double atanh(double x);
18       float atanhf(float x);
19       long double atanhl(long double x);
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21

DESCRIPTION

23       These functions shall compute the inverse hyperbolic tangent  of  their
24       argument x.
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26       An  application  wishing to check for error situations should set errno
27       to zero and  call  feclearexcept(FE_ALL_EXCEPT)  before  calling  these
28       functions.   On return, if errno is non-zero or fetestexcept(FE_INVALID
29       | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error  has
30       occurred.
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RETURN VALUE

33       Upon  successful  completion,  these functions shall return the inverse
34       hyperbolic tangent of their argument.
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36       If x is ±1, a pole  error  shall  occur,  and  atanh(),  atanhf(),  and
37       atanhl()  shall  return the value of the macro HUGE_VAL, HUGE_VALF, and
38       HUGE_VALL, respectively, with the same sign as the correct value of the
39       function.
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41       For  finite  |x|>1,  a  domain error shall occur, and  either a NaN (if
42       supported), or an implementation-defined value shall be returned.
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44       If x is NaN, a NaN shall be returned.
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46       If x is ±0, x shall be returned.
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48       If x is ±Inf, a domain error shall occur, and either  a  NaN  (if  sup‐
49       ported), or an implementation-defined value shall be returned.
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51       If x is subnormal, a range error may occur and x should be returned.
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ERRORS

54       These functions shall fail if:
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56       Domain Error
57              The  x  argument  is  finite and not in the range [-1,1],  or is
58              ±Inf.
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60       If the integer expression (math_errhandling & MATH_ERRNO) is  non-zero,
61       then   errno  shall  be  set  to  [EDOM].  If  the  integer  expression
62       (math_errhandling &  MATH_ERREXCEPT)  is  non-zero,  then  the  invalid
63       floating-point exception shall be raised.
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65       Pole Error
66              The x argument is ±1.
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68       If  the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
69       then errno  shall  be  set  to  [ERANGE].  If  the  integer  expression
70       (math_errhandling  &  MATH_ERREXCEPT)  is non-zero, then the divide-by-
71       zero floating-point exception shall be raised.
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75       These functions may fail if:
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77       Range Error
78              The value of x is subnormal.
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80       If the integer expression (math_errhandling & MATH_ERRNO) is  non-zero,
81       then  errno  shall  be  set  to  [ERANGE].  If  the  integer expression
82       (math_errhandling & MATH_ERREXCEPT) is  non-zero,  then  the  underflow
83       floating-point exception shall be raised.
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86       The following sections are informative.
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EXAMPLES

89       None.
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APPLICATION USAGE

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

97       None.
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FUTURE DIRECTIONS

100       None.
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SEE ALSO

103       feclearexcept(), fetestexcept(), tanh(), the Base Definitions volume of
104       IEEE Std 1003.1-2001, Section 4.18, Treatment of Error  Conditions  for
105       Mathematical Functions, <math.h>
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108       Portions  of  this text are reprinted and reproduced in electronic form
109       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
110       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
111       Specifications Issue 6, Copyright (C) 2001-2003  by  the  Institute  of
112       Electrical  and  Electronics  Engineers, Inc and The Open Group. In the
113       event of any discrepancy between this version and the original IEEE and
114       The  Open Group Standard, the original IEEE and The Open Group Standard
115       is the referee document. The original Standard can be  obtained  online
116       at http://www.opengroup.org/unix/online.html .
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120IEEE/The Open Group                  2003                            ATANH(3P)
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