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man:atan

ATAN(3) Linux Programmer's Manual ATAN(3)

NAME

`     atan, atanf, atanl - arc tangent function`

SYNOPSIS

`     #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)):`
```     atanf(), atanl():
_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 x;
that is the value whose tangent is x.```

RETURN VALUE

```     On success, these functions return the principal value of the arc  tan-
gent 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.```

ERRORS

`     No errors occur.`

ATTRIBUTES

```     For  an  explanation  of  the  terms  used   in   this   section,   see
attributes(7).```
```     +-------------------------+---------------+---------+
|Interface                | Attribute     | Value   |
+-------------------------+---------------+---------+
|atan(), atanf(), atanl() | Thread safety | MT-Safe |
+-------------------------+---------------+---------+```

CONFORMING TO

`     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)`
```     This page is part of release 4.16 of the Linux  man-pages  project.   A
`                                2017-09-15                           ATAN(3)`