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           _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
26       y/x, using the signs of the two arguments to determine the quadrant  of
27       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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ATTRIBUTES

66       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
67       tributes(7).
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69       ┌────────────────────────────────────────────┬───────────────┬─────────┐
70       │Interface                                   │ Attribute     │ Value   │
71       ├────────────────────────────────────────────┼───────────────┼─────────┤
72       │atan2(), atan2f(), atan2l()                 │ Thread safety │ MT-Safe │
73       └────────────────────────────────────────────┴───────────────┴─────────┘
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CONFORMING TO

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

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

84       This page is part of release 5.12 of the Linux  man-pages  project.   A
85       description  of  the project, information about reporting bugs, and the
86       latest    version    of    this    page,    can     be     found     at
87       https://www.kernel.org/doc/man-pages/.
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91                                  2021-03-22                          ATAN2(3)
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