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)):

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.

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