# cis
> Compute the [cis][cis] function of a complex number.
The [cis][cis] function is defined as
## Usage
```javascript
var cis = require( '@stdlib/math/base/special/ccis' );
```
#### cis( \[out,] re, im )
Evaluates the [cis][cis] function with a `complex` argument comprised of a **real** component `re` and an **imaginary** component `im`.
```javascript
var v = cis( 0.0, 0.0 );
// returns [ 1.0, 0.0 ]
v = cis( 1.0, 0.0 );
// returns [ ~0.540, ~0.841 ]
```
By default, the function returns real and imaginary components as a two-element `array`. To avoid unnecessary memory allocation, the function supports providing an output (destination) object.
```javascript
var Float64Array = require( '@stdlib/array/float64' );
var out = new Float64Array( 2 );
var v = cis( out, 1.0, 0.0 );
// returns [ ~0.540, ~0.841 ]
var bool = ( v === out );
// returns true
```
## Examples
```javascript
var Complex128 = require( '@stdlib/complex/float64' );
var randu = require( '@stdlib/random/base/randu' );
var round = require( '@stdlib/math/base/special/round' );
var real = require( '@stdlib/complex/real' );
var imag = require( '@stdlib/complex/imag' );
var cis = require( '@stdlib/math/base/special/ccis' );
var re;
var im;
var z1;
var z2;
var o;
var i;
for ( i = 0; i < 100; i++ ) {
re = round( randu()*100.0 ) - 50.0;
im = round( randu()*100.0 ) - 50.0;
z1 = new Complex128( re, im );
o = cis( [ 0.0, 0.0 ], real(z1), imag(z1) );
z2 = new Complex128( o[ 0 ], o[ 1 ] );
console.log( 'cis(%s) = %s', z1.toString(), z2.toString() );
}
```
[cis]: https://en.wikipedia.org/wiki/Cis_%28mathematics%29
