atan2l(3)

1atan2(3)                   Library Functions Manual                   atan2(3)
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NAME

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

9       Math library (libm, -lm)
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SYNOPSIS

12       #include <math.h>
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14       double atan2(double y, double x);
15       float atan2f(float y, float x);
16       long double atan2l(long double y, long double x);
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18   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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20       atan2f(), atan2l():
21           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
22               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
23               || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
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DESCRIPTION

26       These  functions  calculate  the  principal value of the arc tangent of
27       y/x, using the signs of the two arguments to determine the quadrant  of
28       the result.
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RETURN VALUE

31       On  success, these functions return the principal value of the arc tan‐
32       gent of y/x in radians; the return value is in the range [-pi, pi].
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34       If y is +0 (-0) and x is less than 0, +pi (-pi) is returned.
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36       If y is +0 (-0) and x is greater than 0, +0 (-0) is returned.
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38       If y is less than 0 and x is +0 or -0, -pi/2 is returned.
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40       If y is greater than 0 and x is +0 or -0, pi/2 is returned.
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42       If either x or y is NaN, a NaN is returned.
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44       If y is +0 (-0) and x is -0, +pi (-pi) is returned.
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46       If y is +0 (-0) and x is +0, +0 (-0) is returned.
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48       If y is a finite value greater (less) than 0, and x is negative  infin‐
49       ity, +pi (-pi) is returned.
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51       If  y is a finite value greater (less) than 0, and x is positive infin‐
52       ity, +0 (-0) is returned.
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54       If y is positive infinity (negative infinity), and x  is  finite,  pi/2
55       (-pi/2) is returned.
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57       If  y is positive infinity (negative infinity) and x is negative infin‐
58       ity, +3*pi/4 (-3*pi/4) is returned.
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60       If y is positive infinity (negative infinity) and x is positive  infin‐
61       ity, +pi/4 (-pi/4) is returned.
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ERRORS

64       No errors occur.
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ATTRIBUTES

67       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
68       tributes(7).
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70       ┌────────────────────────────────────────────┬───────────────┬─────────┐
71       │Interface                                   │ Attribute     │ Value   │
72       ├────────────────────────────────────────────┼───────────────┼─────────┤
73       │atan2(), atan2f(), atan2l()                 │ Thread safety │ MT-Safe │
74       └────────────────────────────────────────────┴───────────────┴─────────┘
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STANDARDS

77       C11, POSIX.1-2008.
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HISTORY

80       C99, POSIX.1-2001.
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82       The variant returning double also conforms to SVr4, 4.3BSD, C89.
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