# Archavercosine
> Compute the [inverse half-value versed cosine][archavercosine].
The [inverse half-value versed cosine][archavercosine] is defined as
## Usage
```javascript
var ahavercos = require( '@stdlib/math/base/special/ahavercos' );
```
#### ahavercos( x )
Computes the [inverse half-value versed cosine][archavercosine].
```javascript
var v = ahavercos( 0.0 );
// returns ~3.1416
v = ahavercos( 1.0 );
// returns 0.0
v = ahavercos( 0.5 );
// returns ~1.5708
```
If `x < 0`, `x > 1`, or `x` is `NaN`, the function returns `NaN`.
```javascript
var v = ahavercos( 1.5 );
// returns NaN
v = ahavercos( -3.14 );
// returns NaN
v = ahavercos( NaN );
// returns NaN
```
## Examples
```javascript
var linspace = require( '@stdlib/array/linspace' );
var ahavercos = require( '@stdlib/math/base/special/ahavercos' );
var x = linspace( 0.0, 1.0, 100 );
var i;
for ( i = 0; i < x.length; i++ ) {
console.log( ahavercos( x[ i ] ) );
}
```
[archavercosine]: https://en.wikipedia.org/wiki/Versine
