# atanh
> Compute the [hyperbolic arctangent][hyperbolic-arctangent] of a number.
## Usage
```javascript
var atanh = require( '@stdlib/math/base/special/atanh' );
```
#### atanh( x )
Computes the [hyperbolic arctangent][hyperbolic-arctangent] of a `number` (in radians).
```javascript
var v = atanh( 0.0 );
// returns 0.0
v = atanh( -0.0 );
// returns -0.0
v = atanh( 0.5 );
// returns ~0.549
v = atanh( 0.9 );
// returns ~1.472
v = atanh( 1.0 );
// returns Infinity
v = atanh( -1.0 );
// returns -Infinity
```
The domain of `x` is restricted to `[-1,1]`. If `|x| > 1`, the function returns `NaN`.
```javascript
var v = atanh( -3.14 );
// returns NaN
```
## Examples
```javascript
var linspace = require( '@stdlib/array/linspace' );
var atanh = require( '@stdlib/math/base/special/atanh' );
var x = linspace( -1.0, 1.0, 103 );
var i;
for ( i = 0; i < x.length; i++ ) {
console.log( atanh( x[ i ] ) );
}
```
[hyperbolic-arctangent]: https://en.wikipedia.org/wiki/Inverse_hyperbolic_function