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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():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

```

#### DESCRIPTION

```       These  functions  calculate 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.

```

#### ATTRIBUTES

```       For an explanation of the terms used in this section, see attributes(7).

┌─────────────────────────────┬───────────────┬─────────┐
│Interface                    │ Attribute     │ Value   │
├─────────────────────────────┼───────────────┼─────────┤
│atan2(), atan2f(), atan2l()  │ Thread safety │ MT-Safe │
└─────────────────────────────┴───────────────┴─────────┘
```

#### CONFORMINGTO

```       C99, POSIX.1-2001, POSIX.1-2008.

The variant returning double also conforms to SVr4, 4.3BSD, C89.

```

#### SEEALSO

```       acos(3), asin(3), atan(3), carg(3), cos(3), sin(3), tan(3)

```

#### COLOPHON

```       This  page  is  part of release 5.10 of the Linux man-pages project.  A description of the