1ATAN2(3)                   Linux Programmer's Manual                  ATAN2(3)
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NAME

6       atan2, atan2f, atan2l - arc tangent function of two variables
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SYNOPSIS

9       #include <math.h>
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11       double atan2(double y, double x);
12       float atan2f(float y, float x);
13       long double atan2l(long double y, 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       atan2f(), atan2l():
20              _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 ||
21              _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
22              or cc -std=c99
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DESCRIPTION

25       The atan2() function calculates the principal value of the arc  tangent
26       of  y/x, using the signs of the two arguments to determine the quadrant
27       of the result.
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RETURN VALUE

30       On success, these functions return the principal value of the arc  tan‐
31       gent of y/x in radians; the return value is in the range [-pi, pi].
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33       If y is +0 (-0) and x is less than 0, +pi (-pi) is returned.
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35       If y is +0 (-0) and x is greater than 0, +0 (-0) is returned.
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37       If y is less than 0 and x is +0 or -0, -pi/2 is returned.
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39       If y is greater than 0 and x is +0 or -0, pi/2 is returned.
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41       If either x or y is NaN, a NaN is returned.
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43       If y is +0 (-0) and x is -0, +pi (-pi) is returned.
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45       If y is +0 (-0) and x is +0, +0 (-0) is returned.
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47       If  y is a finite value greater (less) than 0, and x is negative infin‐
48       ity, +pi (-pi) is returned.
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50       If y is a finite value greater (less) than 0, and x is positive  infin‐
51       ity, +0 (-0) is returned.
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53       If  y  is  positive infinity (negative infinity), and x is finite, pi/2
54       (-pi/2) is returned.
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56       If y is positive infinity (negative infinity) and x is negative  infin‐
57       ity, +3*pi/4 (-3*pi/4) is returned.
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59       If  y is positive infinity (negative infinity) and x is positive infin‐
60       ity, +pi/4 (-pi/4) is returned.
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ERRORS

63       No errors occur.
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CONFORMING TO

66       C99, POSIX.1-2001.  The variant returning double also conforms to SVr4,
67       4.3BSD, C89.
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SEE ALSO

70       acos(3), asin(3), atan(3), carg(3), cos(3), sin(3), tan(3)
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COLOPHON

73       This  page  is  part of release 3.53 of the Linux man-pages project.  A
74       description of the project, and information about reporting  bugs,  can
75       be found at http://www.kernel.org/doc/man-pages/.
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79                                  2010-09-20                          ATAN2(3)
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