1ATAN(P)                    POSIX Programmer's Manual                   ATAN(P)
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NAME

6       atan, atanf, atanl - arc tangent function
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SYNOPSIS

9       #include <math.h>
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11       double atan(double x);
12       float atanf(float x);
13       long double atanl(long double x);
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DESCRIPTION

17       These functions shall compute the principal value of the arc tangent of
18       their argument x.
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20       An application wishing to check for error situations should  set  errno
21       to  zero  and  call  feclearexcept(FE_ALL_EXCEPT)  before calling these
22       functions.  On return, if errno is non-zero or  fetestexcept(FE_INVALID
23       |  FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has
24       occurred.
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RETURN VALUE

27       Upon successful completion, these functions shall return the  arc  tan‐
28       gent of x in the range [-pi/2,pi/2] radians.
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30       If x is NaN, a NaN shall be returned.
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32       If x is ±0, x shall be returned.
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34       If x is ±Inf, ±pi/2 shall be returned.
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36       If x is subnormal, a range error may occur and x should be returned.
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ERRORS

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

53       None.
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APPLICATION USAGE

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

61       None.
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FUTURE DIRECTIONS

64       None.
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SEE ALSO

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