Open Source Software

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
   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  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 4.09 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/.

                              2016-03-15                          ATAN2(3)



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