Provided by: manpages-dev_3.35-0.1ubuntu1_all NAME

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

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():
_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.

RETURNVALUE

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.

CONFORMINGTO

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

SEEALSO

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

COLOPHON

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project,  and information about reporting bugs, can be found at http://man7.org/linux/man-
pages/.

2010-09-20                                   ATAN2(3)