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ATAN2(3)                   Linux Programmer's Manual                  ATAN2(3)



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);

       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; 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 argu-
       ments 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
       This  page  is part of release 3.22 of the Linux man-pages project.  A description of the project, and informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



                                  2008-11-20                          ATAN2(3)