atan, atanf, atanl - arc tangent function

```
#include <math.h>
double atan(double x);
float atanf(float x);
long double atanl( long double x);
```

Link with `-lm`

.

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

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

These functions calculate the principal value of the arc tangent of `x`

; that is the value whose tangent is `x`

.

On success, these functions return the principal value of the arc tangent of `x`

in radians; the return value is in the range [-pi/2, pi/2].

If `x`

is a NaN, a NaN is returned.

If `x`

is +0 (-0), +0 (-0) is returned.

If `x`

is positive infinity (negative infinity), +pi/2 (-pi/2) is returned.

No errors occur.

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

Interface | Attribute | Value |

atan(), atanf(), atanl() | Thread safety | MT-Safe |

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

The variant returning `double`

also conforms to SVr4, 4.3BSD, C89.

acos(3), asin(3), atan2(3), carg(3), catan(3), cos(3), sin(3), tan(3)

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