1ATAN(3)                    Linux Programmer's Manual                   ATAN(3)
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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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15       Link with -lm.
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17   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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19       atanf(), atanl():
20           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
21               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
22               || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
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DESCRIPTION

25       These  functions calculate the principal value of the arc tangent of x;
26       that is the value whose tangent is x.
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RETURN VALUE

29       On success, these functions return the principal value of the arc  tan‐
30       gent of x in radians; the return value is in the range [-pi/2, pi/2].
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32       If x is a NaN, a NaN is returned.
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34       If x is +0 (-0), +0 (-0) is returned.
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36       If  x  is  positive  infinity (negative infinity), +pi/2 (-pi/2) is re‐
37       turned.
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ERRORS

40       No errors occur.
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ATTRIBUTES

43       For an  explanation  of  the  terms  used  in  this  section,  see  at‐
44       tributes(7).
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46       ┌────────────────────────────────────────────┬───────────────┬─────────┐
47       │Interface                                   │ Attribute     │ Value   │
48       ├────────────────────────────────────────────┼───────────────┼─────────┤
49       │atan(), atanf(), atanl()                    │ Thread safety │ MT-Safe │
50       └────────────────────────────────────────────┴───────────────┴─────────┘
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CONFORMING TO

53       C99, POSIX.1-2001, POSIX.1-2008.
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55       The variant returning double also conforms to SVr4, 4.3BSD, C89.
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SEE ALSO

58       acos(3), asin(3), atan2(3), carg(3), catan(3), cos(3), sin(3), tan(3)
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COLOPHON

61       This  page  is  part of release 5.13 of the Linux man-pages project.  A
62       description of the project, information about reporting bugs,  and  the
63       latest     version     of     this    page,    can    be    found    at
64       https://www.kernel.org/doc/man-pages/.
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68                                  2021-03-22                           ATAN(3)
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