Content-type: text/html Man page of atan2

# atan2

Section: Mathematical Library Functions (3M)
Updated: 12 Jul 2006

## 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

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUES
ERRORS
ATTRIBUTES