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# atanh

> Compute the [hyperbolic arctangent][hyperbolic-arctangent] of a number.

<section class="usage">

## 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
```

</section>

<!-- /.usage -->

<section class="examples">

## Examples

<!-- eslint no-undef: "error" -->

```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 ] ) );
}
```

</section>

<!-- /.examples -->

<section class="links">

[hyperbolic-arctangent]: https://en.wikipedia.org/wiki/Inverse_hyperbolic_function

</section>

<!-- /.links -->