Manual Reference Pages - ATAN2 (3)
NAME
atan2, atan2f, atan2l - arc tangent function of two variables
CONTENTS
Synopsis
Description
Errors
Colophon
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 );

Link with -lm .
Feature Test Macro Requirements for glibc (see
feature_test_macros (7)):

atan2f (),
atan2l ():

_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;
or
cc -std=c99
DESCRIPTION
The
atan2 () function calculates 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.
CONFORMING TO
C99, POSIX.1-2001.
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)
COLOPHON
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A description of the project,
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