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(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600
20       || _ISOC99_SOURCE; or cc -std=c99
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DESCRIPTION

23       The atan() function calculates the principal value of the  arc  tangent
24       of x; that is the value whose tangent is x.
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RETURN VALUE

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

38       No errors occur.
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CONFORMING TO

41       C99, POSIX.1-2001.  The variant returning double also conforms to SVr4,
42       4.3BSD, C89.
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SEE ALSO

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

48       This page is part of release 3.25 of the Linux  man-pages  project.   A
49       description  of  the project, and information about reporting bugs, can
50       be found at http://www.kernel.org/doc/man-pages/.
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54                                  2008-12-02                           ATAN(3)