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## 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);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

atan2f(), atan2l(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600
|| _ISOC99_SOURCE; or cc -std=c99

```

## DESCRIPTION

```       The atan2() function calculates the principal value of the arc  tangent
of  y/x, using the signs of the two arguments to determine the quadrant
of the result.

```

## RETURNVALUE

```       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.

```

## CONFORMINGTO

```       C99, POSIX.1-2001.  The variant returning double also conforms to SVr4,
4.3BSD, C89.

```

```       acos(3), asin(3), atan(3), carg(3), cos(3), sin(3), tan(3)
```       This page is part of release 3.24 of the Linux  man-pages  project.   A