opensolaris man page for atan2

atan2(3M)						  Mathematical Library Functions						 atan2(3M)

NAME
       atan2, atan2f, atan2l - arc tangent function

SYNOPSIS
       c99 [ flag... ] file... -lm [ library... ]
       #include <math.h>

       double atan2(double y, double x);

       float atan2f(float y, float x);

       long double atan2l(long double y, long double x);

DESCRIPTION
       These  functions  compute the principal value of the arc tangent of y/x, using the signs of both arguments to determine the quadrant of the
       return value.

RETURN VALUES
       Upon successful completion, these functions return the arc tangent of y/x in the range [ -pi,pi ] radians.

       If y is +-0 and x is < 0, +-pi is returned.

       If y is +-0 and x is > 0, +-0 is returned.

       If y is < 0 and x is +-0, -pi/2 is returned.

       If y is > 0 and x is +-0, pi/2 is returned.

       If x is 0, a pole error does not occur.

       If either x or y is NaN, a NaN is returned.

       If y is +-0 and x is -0, +-pi is returned.

       If y is +-0 and x is +0, +-0 is returned.

       For finite values of +-y > 0, if x is -Inf,  +-pi is returned.

       For finite values of +-y > 0, if x is +Inf,  +-0 is returned.

       For finite values of x, if y is +-Inf, +-pi/2 is returned.

       If y is +-Inf and x is -Inf, +-3pi/4 is returned.

       If y is +-Inf and x is +Inf, +-pi/4 is returned.

       If both arguments are 0, a domain error does not occur.

ERRORS
       No errors are defined.

ATTRIBUTES
       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Standard			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |MT-Safe			   |
       +-----------------------------+-----------------------------+

SEE ALSO
       atan(3M), isnan(3M), math.h(3HEAD)tan(3M), attributes(5), standards(5)

SunOS 5.11							    12 Jul 2006 							 atan2(3M)