NAME

atan2 − arc tangent function

SYNOPSIS

cc [ flag ... ] file ... −lm [ library ... ]

#include <math.h>

double atan2(double y, double x);

DESCRIPTION

The atan2() function computes 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, atan2() returns the arc tangent of y/x in the range [−π,π] radians.  If both arguments are 0.0, 0.0 is returned and errno may be set to EDOM. 

If x or y is NaN, NaN is returned. 

In IEEE754 mode (the −xlibmieee cc compilation option), atan2() handles the following exceptional arguments in the spirit of ANSI/IEEE Std 754-1985. 

atan2(±0,x) returns ±0 for x > 0 or x = +0;
atan2(±0,x) returns ±π for x < 0 or x = −0;
atan2(y,±0) returns π/2 for y > 0;
atan2(y,±0) returns −π/2 for y < 0;
atan2(±y,Inf) returns ±0 for finite y > 0;
atan2(±Inf,x) returns ±π/2 for finite x;
atan2(±y,−Inf) returns ±π for finite y > 0;
atan2(±Inf,Inf) returns ±π/4;
atan2(±Inf,−Inf) returns ±3π/4. 

For exceptional cases, matherr(3M) tabulates the values to be returned as dictated by Standards other than XPG4. 

ERRORS

The atan2() function may fail if:

EDOM Both arguments are 0.0. 

USAGE

An application wishing to check for error situations should set errno to 0 before calling atan2().  If errno is non-zero on return, or the return value is NaN, an error has occurred. 

ATTRIBUTES

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

SEE ALSO

atan(3M), isnan(3M), matherr(3M), tan(3M), attributes(5), standards(5)

SunOS 5.6  —  Last change: 29 Dec 1996