# 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 realf = require( '@stdlib/complex/float32/real' );
var imagf = require( '@stdlib/complex/float32/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 = realf( z );
// returns 1.0
var im = imagf( z );
// returns 2.0
z = x.get( 0 );
// returns
re = realf( z );
// returns 0.0
im = imagf( z );
// returns 0.0
```
The function has the following parameters:
- **N**: number of indexed elements.
- **x**: first input [`Complex64Array`][@stdlib/array/complex64].
- **strideX**: index increment for `x`.
- **y**: second input [`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 realf = require( '@stdlib/complex/float32/real' );
var imagf = require( '@stdlib/complex/float32/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 ] );
cswap( 2, x, -2, y, 1 );
var z = y.get( 0 );
// returns
var re = realf( z );
// returns 5.0
var im = imagf( z );
// returns 6.0
z = x.get( 0 );
// returns
re = realf( z );
// returns 0.0
im = imagf( 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 realf = require( '@stdlib/complex/float32/real' );
var imagf = require( '@stdlib/complex/float32/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
// Interchange in reverse order every other value from `x1` into `y1`...
cswap( 2, x1, -2, y1, 1 );
var z = y0.get( 2 );
// returns
var re = realf( z );
// returns 7.0
var im = imagf( z );
// returns 8.0
z = x0.get( 1 );
// returns
re = realf( z );
// returns 0.0
im = imagf( 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 realf = require( '@stdlib/complex/float32/real' );
var imagf = require( '@stdlib/complex/float32/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 = realf( z );
// returns 1.0
var im = imagf( z );
// returns 2.0
z = x.get( 0 );
// returns
re = realf( z );
// returns 0.0
im = imagf( 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 offset 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 realf = require( '@stdlib/complex/float32/real' );
var imagf = require( '@stdlib/complex/float32/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 ] );
cswap.ndarray( 2, x, 2, 1, y, -1, y.length-1 );
var z = y.get( y.length-1 );
// returns
var re = realf( z );
// returns 3.0
var im = imagf( z );
// returns 4.0
z = x.get( x.length-1 );
// returns
re = realf( z );
// returns 0.0
im = imagf( 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 filledarrayBy = require( '@stdlib/array/filled-by' );
var Complex64 = require( '@stdlib/complex/float32/ctor' );
var cswap = require( '@stdlib/blas/base/cswap' );
function rand() {
return new Complex64( discreteUniform( 0, 10 ), discreteUniform( -5, 5 ) );
}
var x = filledarrayBy( 10, 'complex64', rand );
console.log( x.get( 0 ).toString() );
var y = filledarrayBy( 10, 'complex64', rand );
console.log( y.get( 0 ).toString() );
// Swap elements in `x` into `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() );
```
* * *
## C APIs
### Usage
```c
#include "stdlib/blas/base/cswap.h"
```
#### c_cswap( N, \*X, strideX, \*Y, strideY )
Interchanges two complex single-precision floating-point vectors.
```c
float x[] = { 1.0f, 2.0f, 3.0f, 4.0f }; // interleaved real and imaginary components
float y[] = { 5.0f, 6.0f, 7.0f, 8.0f };
c_cswap( 2, (void *)x, 1, (void *)Y, 1 );
```
The function accepts the following arguments:
- **N**: `[in] CBLAS_INT` number of indexed elements.
- **X**: `[inout] void*` first input array.
- **strideX**: `[in] CBLAS_INT` index increment for `X`.
- **Y**: `[inout] void*` first input array.
- **strideY**: `[in] CBLAS_INT` index increment for `Y`.
```c
void c_cswap( const CBLAS_INT N, void *X, const CBLAS_INT strideX, void *Y, const CBLAS_INT strideY );
```
### Examples
```c
#include "stdlib/blas/base/cswap.h"
#include
int main( void ) {
// Create strided arrays:
float x[] = { 1.0f, 2.0f, 3.0f, 4.0f, 5.0f, 6.0f, 7.0f, 8.0f };
float y[] = { 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f };
// Specify the number of elements:
const int N = 4;
// Specify stride lengths:
const int strideX = 1;
const int strideY = -1;
// Copy elements:
c_cswap( N, (void *)x, strideX, (void *)y, strideY );
// Print the result:
for ( int i = 0; i < N; i++ ) {
printf( "x[ %i ] = %f + %fj\n", i, x[ i*2 ], x[ (i*2)+1 ] );
printf( "y[ %i ] = %f + %fj\n", i, y[ i*2 ], y[ (i*2)+1 ] );
}
}
```
[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
[@stdlib/blas/base/ccopy]: https://github.com/stdlib-js/blas/tree/main/base/ccopy