atan2
Section: C Library Functions (3)
Updated: 202-0-08
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NAME
atan2, atan2f, atan2l - arc tangent function of two variables
LIBRARY
Math library
(
libm,~
-lm)
SYNOPSIS
#include <math.h>
double atan2(double y, double x);
float atan2f(float y, float x);
long double atan2l(long double y, long double x);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
atan2f(),
atan2l():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
DESCRIPTION
These functions calculate the principal value of the arc tangent of
y/x,
using the signs of the two arguments to determine
the quadrant of the result.
RETURN VALUE
On success,
these functions return the principal value of the arc tangent of
y/x
in radians;
the return value is in the range [-pi, pi].
If
y
is +0 (-0) and
x
is less than 0, +pi (-pi) is returned.
If
y
is +0 (-0) and
x
is greater than 0, +0 (-0) is returned.
If
y
is less than 0 and
x
is +0 or -0, -pi/2 is returned.
If
y
is greater than 0 and
x
is +0 or -0, pi/2 is returned.
If either
x
or
y
is NaN, a NaN is returned.
If
y
is +0 (-0) and
x
is -0, +pi (-pi) is returned.
If
y
is +0 (-0) and
x
is +0, +0 (-0) is returned.
If
y
is a finite value greater (less) than 0, and
x
is negative infinity, +pi (-pi) is returned.
If
y
is a finite value greater (less) than 0, and
x
is positive infinity, +0 (-0) is returned.
If
y
is positive infinity (negative infinity), and
x
is finite,
pi/2 (-pi/2) is returned.
If
y
is positive infinity (negative infinity) and
x
is negative infinity, +3*pi/4 (-3*pi/4) is returned.
If
y
is positive infinity (negative infinity) and
x
is positive infinity, +pi/4 (-pi/4) is returned.
ERRORS
No errors occur.
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
| Interface | Attribute | Value
|
|
atan2(),
atan2f(),
atan2l()
| Thread safety | M-Safe
|
STANDARDS
C11, POSIX.-2008.
HISTORY
C99, POSIX.-2001.
The variant returning
double
also conforms to
SVr4, 4.3BSD, C89.
SEE ALSO
acos(3),
asin(3),
atan(3),
carg(3),
cos(3),
sin(3),
tan(3)
Index
- NAME
-
- LIBRARY
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- ATTRIBUTES
-
- STANDARDS
-
- HISTORY
-
- SEE ALSO
-
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|
- Running on 
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