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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():
              _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
                  || /* Since glibc 2.19: */ _DEFAULT_SOURCE
                  || /* Glibc versions <= 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 tan-
       gent 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  infin-
       ity, +pi (-pi) is returned.
       If  y is a finite value greater (less) than 0, and x is positive infin-
       ity, +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 infin-
       ity, +3*pi/4 (-3*pi/4) is returned.
       If y is positive infinity (negative infinity) and x is positive  infin-
       ity, +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 | MT-Safe |
       +-----------------------------+---------------+---------+
CONFORMING TO
       C99, POSIX.1-2001, POSIX.1-2008.
       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 4.15 of the Linux  man-pages  project.   A
       description  of  the project, information about reporting bugs, and the
       latest    version    of    this    page,    can     be     found     at
       https://www.kernel.org/doc/man-pages/.
                                  2017-09-15                          ATAN2(3)