# cswap
> Interchange two complex single-precision floating-point vectors.
## Usage
```javascript
var cswap = require( '@stdlib/blas/base/cswap' );
```
#### cswap( N, x, strideX, y, strideY )
Interchanges two complex single-precision floating-point vectors.
```javascript
var Complex64Array = require( '@stdlib/array/complex64' );
var real = require( '@stdlib/complex/real' );
var imag = require( '@stdlib/complex/imag' );
var x = new Complex64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );
var y = new Complex64Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );
cswap( x.length, x, 1, y, 1 );
var z = y.get( 0 );
// returns
var re = real( z );
// returns 1.0
var im = imag( z );
// returns 2.0
z = x.get( 0 );
// returns
re = real( z );
// returns 0.0
im = imag( z );
// returns 0.0
```
The function has the following parameters:
- **N**: number of values to swap.
- **x**: input [`Complex64Array`][@stdlib/array/complex64].
- **strideX**: index increment for `x`.
- **y**: destination [`Complex64Array`][@stdlib/array/complex64].
- **strideY**: index increment for `y`.
The `N` and `stride` parameters determine how values from `x` are interchanged with values from `y`. For example, to interchange in reverse order every other value in `x` into the first `N` elements of `y`,
```javascript
var Complex64Array = require( '@stdlib/array/complex64' );
var floor = require( '@stdlib/math/base/special/floor' );
var real = require( '@stdlib/complex/real' );
var imag = require( '@stdlib/complex/imag' );
var x = new Complex64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0 ] );
var y = new Complex64Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );
var N = floor( x.length / 2 );
cswap( N, x, -2, y, 1 );
var z = y.get( 0 );
// returns
var re = real( z );
// returns 5.0
var im = imag( z );
// returns 6.0
z = x.get( 0 );
// returns
re = real( z );
// returns 0.0
im = imag( z );
// returns 0.0
```
Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][mdn-typed-array] views.
```javascript
var Complex64Array = require( '@stdlib/array/complex64' );
var floor = require( '@stdlib/math/base/special/floor' );
var real = require( '@stdlib/complex/real' );
var imag = require( '@stdlib/complex/imag' );
// Initial arrays...
var x0 = new Complex64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0 ] );
var y0 = new Complex64Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );
// Create offset views...
var x1 = new Complex64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
var y1 = new Complex64Array( y0.buffer, y0.BYTES_PER_ELEMENT*2 ); // start at 3rd element
var N = floor( x0.length / 2 );
// Interchange in reverse order every other value from `x1` into `y1`...
cswap( N, x1, -2, y1, 1 );
var z = y0.get( 2 );
// returns
var re = real( z );
// returns 7.0
var im = imag( z );
// returns 8.0
z = x0.get( 1 );
// returns
re = real( z );
// returns 0.0
im = imag( z );
// returns 0.0
```
#### cswap.ndarray( N, x, strideX, offsetX, y, strideY, offsetY )
Interchanges two complex single-precision floating-point vectors using alternative indexing semantics.
```javascript
var Complex64Array = require( '@stdlib/array/complex64' );
var real = require( '@stdlib/complex/real' );
var imag = require( '@stdlib/complex/imag' );
var x = new Complex64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );
var y = new Complex64Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );
cswap.ndarray( x.length, x, 1, 0, y, 1, 0 );
var z = y.get( 0 );
// returns
var re = real( z );
// returns 1.0
var im = imag( z );
// returns 2.0
z = x.get( 0 );
// returns
re = real( z );
// returns 0.0
im = imag( z );
// returns 0.0
```
The function has the following additional parameters:
- **offsetX**: starting index for `x`.
- **offsetY**: starting index for `y`.
While [`typed array`][mdn-typed-array] views mandate a view offset based on the underlying `buffer`, the `offsetX` and `offsetY` parameters support indexing semantics based on starting indices. For example, to interchange every other value in `x` starting from the second value into the last `N` elements in `y` where `x[i] = y[n]`, `x[i+2] = y[n-1]`,...,
```javascript
var Complex64Array = require( '@stdlib/array/complex64' );
var floor = require( '@stdlib/math/base/special/floor' );
var real = require( '@stdlib/complex/real' );
var imag = require( '@stdlib/complex/imag' );
var x = new Complex64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0 ] );
var y = new Complex64Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );
var N = floor( x.length / 2 );
cswap.ndarray( N, x, 2, 1, y, -1, y.length-1 );
var z = y.get( y.length-1 );
// returns
var re = real( z );
// returns 3.0
var im = imag( z );
// returns 4.0
z = x.get( x.length-1 );
// returns
re = real( z );
// returns 0.0
im = imag( z );
// returns 0.0
```
## Notes
- If `N <= 0`, both functions leave `x` and `y` unchanged.
- `cswap()` corresponds to the [BLAS][blas] level 1 function [`cswap`][cswap].
## Examples
```javascript
var discreteUniform = require( '@stdlib/random/base/discrete-uniform' );
var Complex64Array = require( '@stdlib/array/complex64' );
var cswap = require( '@stdlib/blas/base/cswap' );
var re = discreteUniform.factory( 0, 10 );
var im = discreteUniform.factory( -5, 5 );
var x = new Complex64Array( 10 );
var y = new Complex64Array( 10 );
var i;
for ( i = 0; i < x.length; i++ ) {
x.set( [ re(), im() ], i );
y.set( [ re(), im() ], i );
}
console.log( x.get( 0 ).toString() );
console.log( y.get( 0 ).toString() );
// Swap elements in `x` and `y` starting from the end of `y`:
cswap( x.length, x, 1, y, -1 );
console.log( x.get( x.length-1 ).toString() );
console.log( y.get( y.length-1 ).toString() );
```
[blas]: http://www.netlib.org/blas
[cswap]: http://www.netlib.org/lapack/explore-html/da/df6/group__complex__blas__level1.html
[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray
[@stdlib/array/complex64]: https://www.npmjs.com/package/@stdlib/array-complex64