# Havercosine
> Compute the half-value [versed cosine][versed-cosine].
The half-value [versed cosine][versed-cosine] is defined as
## Usage
```javascript
var havercos = require( '@stdlib/math/base/special/havercos' );
```
#### havercos( x )
Computes the half-value [versed cosine][versed-cosine] (in radians).
```javascript
var v = havercos( 0.0 );
// returns 1.0
v = havercos( 3.141592653589793/2.0 );
// returns 0.5
v = havercos( -3.141592653589793/6.0 );
// returns ~0.9330
```
## Examples
```javascript
var linspace = require( '@stdlib/array/linspace' );
var TWO_PI = require( '@stdlib/constants/float64/two-pi' );
var havercos = require( '@stdlib/math/base/special/havercos' );
var x = linspace( 0.0, TWO_PI, 100 );
var i;
for ( i = 0; i < x.length; i++ ) {
console.log( havercos( x[ i ] ) );
}
```
[versed-cosine]: https://en.wikipedia.org/wiki/Versine
