time-to-botec/js/node_modules/@stdlib/blas/base/cswap/README.md

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# cswap

> Interchange two complex single-precision floating-point vectors.

<section class="usage">

## 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 <Complex64>

var re = real( z );
// returns 1.0

var im = imag( z );
// returns 2.0

z = x.get( 0 );
// returns <Complex64>

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 <Complex64>

var re = real( z );
// returns 5.0

var im = imag( z );
// returns 6.0

z = x.get( 0 );
// returns <Complex64>

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.

<!-- eslint-disable stdlib/capitalized-comments -->

```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 <Complex64>

var re = real( z );
// returns 7.0

var im = imag( z );
// returns 8.0

z = x0.get( 1 );
// returns <Complex64>

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 <Complex64>

var re = real( z );
// returns 1.0

var im = imag( z );
// returns 2.0

z = x.get( 0 );
// returns <Complex64>

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 <Complex64>

var re = real( z );
// returns 3.0

var im = imag( z );
// returns 4.0

z = x.get( x.length-1 );
// returns <Complex64>

re = real( z );
// returns 0.0

im = imag( z );
// returns 0.0
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

-   If `N <= 0`, both functions leave `x` and `y` unchanged.
-   `cswap()` corresponds to the [BLAS][blas] level 1 function [`cswap`][cswap].

</section>

<!-- /.notes -->

<section class="examples">

## Examples

<!-- eslint no-undef: "error" -->

```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() );
```

</section>

<!-- /.examples -->

<section class="links">

[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

</section>

<!-- /.links -->