1ATAN(3P)                   POSIX Programmer's Manual                  ATAN(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       atan, atanf, atanl - arc tangent function
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SYNOPSIS

15       #include <math.h>
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17       double atan(double x);
18       float atanf(float x);
19       long double atanl(long double x);
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DESCRIPTION

23       These functions shall compute the principal value of the arc tangent of
24       their 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 arc tan‐
34       gent of x in the range [-pi/2,pi/2] radians.
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36       If x is NaN, a NaN shall be returned.
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38       If x is ±0, x shall be returned.
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40       If x is ±Inf, ±pi/2 shall be returned.
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42       If x is subnormal, a range error may occur and x should be returned.
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ERRORS

45       These functions may fail if:
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47       Range Error
48              The value of x is subnormal.
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50       If the integer expression (math_errhandling & MATH_ERRNO) is  non-zero,
51       then  errno  shall  be  set  to  [ERANGE].  If  the  integer expression
52       (math_errhandling & MATH_ERREXCEPT) is  non-zero,  then  the  underflow
53       floating-point exception shall be raised.
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56       The following sections are informative.
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EXAMPLES

59       None.
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APPLICATION USAGE

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

67       None.
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FUTURE DIRECTIONS

70       None.
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SEE ALSO

73       atan2(), feclearexcept(), fetestexcept(), isnan(), tan(), the Base Def‐
74       initions volume of IEEE Std 1003.1-2001,  Section  4.18,  Treatment  of
75       Error Conditions for Mathematical Functions, <math.h>
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78       Portions  of  this text are reprinted and reproduced in electronic form
79       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
80       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
81       Specifications Issue 6, Copyright (C) 2001-2003  by  the  Institute  of
82       Electrical  and  Electronics  Engineers, Inc and The Open Group. In the
83       event of any discrepancy between this version and the original IEEE and
84       The  Open Group Standard, the original IEEE and The Open Group Standard
85       is the referee document. The original Standard can be  obtained  online
86       at http://www.opengroup.org/unix/online.html .
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90IEEE/The Open Group                  2003                             ATAN(3P)
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