# cosm1
> Compute `cos(x) - 1`.
## Usage
```javascript
var cosm1 = require( '@stdlib/math/base/special/cosm1' );
```
#### cosm1( x )
Computes `cos(x) - 1`, where `cos` is the [cosine][@stdlib/math/base/special/cos] of a `number` (in radians). This function should be used instead of manually calculating `cos(x) - 1` when the argument is near unity.
```javascript
var PI = require( '@stdlib/constants/float64/pi' );
var v = cosm1( 0.0 );
// returns 0.0
v = cosm1( PI/4.0 );
// returns ~-0.293
v = cosm1( -PI/6.0 );
// returns ~-0.134
v = cosm1( NaN );
// returns NaN
```
## Examples
```javascript
var linspace = require( '@stdlib/array/linspace' );
var PI = require( '@stdlib/constants/float64/pi' );
var cosm1 = require( '@stdlib/math/base/special/cosm1' );
var x = linspace( 0.0, 2.0*PI, 100 );
var i;
for ( i = 0; i < x.length; i++ ) {
console.log( cosm1( x[ i ] ) );
}
```
[@stdlib/math/base/special/cos]: https://www.npmjs.com/package/@stdlib/math/tree/main/base/special/cos