# cospi
> Compute the [cosine][@stdlib/math/base/special/cos] of a number times [π][@stdlib/constants/float64/pi].
## Usage
```javascript
var cospi = require( '@stdlib/math/base/special/cospi' );
```
#### cospi( x )
Computes `cos(πx)` more accurately than `cos(pi*x)`, especially for large `x`.
```javascript
var y = cospi( 0.0 );
// returns 1.0
y = cospi( 0.5 );
// returns 0.0
y = cospi( 0.1 );
// returns ~0.951
y = cospi( NaN );
// returns NaN
```
## Examples
```javascript
var linspace = require( '@stdlib/array/linspace' );
var cospi = require( '@stdlib/math/base/special/cospi' );
var x = linspace( -100.0, 100.0, 100 );
var i;
for ( i = 0; i < x.length; i++ ) {
console.log( cospi( x[ i ] ) );
}
```
[@stdlib/math/base/special/cos]: https://www.npmjs.com/package/@stdlib/math/tree/main/base/special/cos
[@stdlib/constants/float64/pi]: https://www.npmjs.com/package/@stdlib/constants-float64-pi