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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11

NAME

13       atanh, atanhf, atanhl — inverse hyperbolic tangent functions
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SYNOPSIS

16       #include <math.h>
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18       double atanh(double x);
19       float atanhf(float x);
20       long double atanhl(long double x);
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DESCRIPTION

23       The functionality described on this reference page is aligned with  the
24       ISO C  standard.  Any  conflict between the requirements described here
25       and the ISO C standard is unintentional. This  volume  of  POSIX.1‐2008
26       defers to the ISO C standard.
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28       These  functions  shall compute the inverse hyperbolic tangent of their
29       argument x.
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31       An application wishing to check for error situations should  set  errno
32       to  zero  and  call  feclearexcept(FE_ALL_EXCEPT)  before calling these
33       functions. On return, if errno is non-zero or fetestexcept(FE_INVALID |
34       FE_DIVBYZERO  |  FE_OVERFLOW  | FE_UNDERFLOW) is non-zero, an error has
35       occurred.
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RETURN VALUE

38       Upon successful completion, these functions shall  return  the  inverse
39       hyperbolic tangent of their argument.
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41       If  x  is  ±1,  a  pole  error  shall occur, and atanh(), atanhf(), and
42       atanhl() shall return the value of the macro HUGE_VAL,  HUGE_VALF,  and
43       HUGE_VALL, respectively, with the same sign as the correct value of the
44       function.
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46       For finite |x|>1, a domain error shall occur, and either a NaN (if sup‐
47       ported), or an implementation-defined value shall be returned.
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49       If x is NaN, a NaN shall be returned.
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51       If x is ±0, x shall be returned.
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53       If x is ±Inf, a domain error shall occur, and a NaN shall be returned.
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55       If x is subnormal, a range error may occur
56       and x should be returned.
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58       If  x  is not returned, atanh(), atanhf(), and atanhl() shall return an
59       implementation-defined value no  greater  in  magnitude  than  DBL_MIN,
60       FLT_MIN, and LDBL_MIN, respectively.
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ERRORS

63       These functions shall fail if:
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65       Domain Error
66                   The x argument is finite and not in the range [−1,1], or is
67                   ±Inf.
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69                   If the integer expression (math_errhandling  &  MATH_ERRNO)
70                   is  non-zero,  then  errno  shall be set to [EDOM].  If the
71                   integer expression (math_errhandling &  MATH_ERREXCEPT)  is
72                   non-zero,  then  the invalid floating-point exception shall
73                   be raised.
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75       Pole Error  The x argument is ±1.
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77                   If the integer expression (math_errhandling  &  MATH_ERRNO)
78                   is  non-zero,  then errno shall be set to [ERANGE].  If the
79                   integer expression (math_errhandling &  MATH_ERREXCEPT)  is
80                   non-zero,  then the divide-by-zero floating-point exception
81                   shall be raised.
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83       These functions may fail if:
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85       Range Error The value of x is subnormal.
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87                   If the integer expression (math_errhandling  &  MATH_ERRNO)
88                   is  non-zero,  then errno shall be set to [ERANGE].  If the
89                   integer expression (math_errhandling &  MATH_ERREXCEPT)  is
90                   non-zero, then the underflow floating-point exception shall
91                   be raised.
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93       The following sections are informative.
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EXAMPLES

96       None.
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APPLICATION USAGE

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

104       None.
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FUTURE DIRECTIONS

107       None.
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SEE ALSO

110       feclearexcept(), fetestexcept(), tanh()
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112       The Base Definitions volume of POSIX.1‐2008, Section 4.19, Treatment of
113       Error Conditions for Mathematical Functions, <math.h>
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116       Portions  of  this text are reprinted and reproduced in electronic form
117       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
118       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
119       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
120       cal  and  Electronics  Engineers,  Inc  and  The  Open Group.  (This is
121       POSIX.1-2008 with the 2013 Technical Corrigendum  1  applied.)  In  the
122       event of any discrepancy between this version and the original IEEE and
123       The Open Group Standard, the original IEEE and The Open Group  Standard
124       is  the  referee document. The original Standard can be obtained online
125       at http://www.unix.org/online.html .
126
127       Any typographical or formatting errors that appear  in  this  page  are
128       most likely to have been introduced during the conversion of the source
129       files to man page format. To report such errors,  see  https://www.ker‐
130       nel.org/doc/man-pages/reporting_bugs.html .
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134IEEE/The Open Group                  2013                            ATANH(3P)
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