## Linux and UNIX Man Pages

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# atan2(3m) [opensolaris man page]

```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			   |
+-----------------------------+-----------------------------+