feat: add blas/base/zswap

lib/node_modules/@stdlib/blas/base/zswap/README.md

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+<!--
+
+@license Apache-2.0
+
+Copyright (c) 2024 The Stdlib Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+   http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+
+-->
+
+# zswap
+
+> Interchange two complex double-precision floating-point vectors.
+
+<section class="intro">
+
+This BLAS level 1 routine interchanges complex double-precision floating-point vectors `x` and `y`. The operation is performed in-place, with `x` being overwritten with the values from `y`, and `y` being overwritten with the values from `x`.
+
+</section>
+
+<!-- /.intro -->
+
+<section class="usage">
+
+## Usage
+
+```javascript
+var zswap = require( '@stdlib/blas/base/zswap' );
+```
+
+#### zswap( N, x, strideX, y, strideY )
+
+Interchange two complex double-precision floating-point vectors.
+
+```javascript
+var Complex128Array = require( '@stdlib/array/complex128' );
+var real = require( '@stdlib/complex/real' );
+var imag = require( '@stdlib/complex/imag' );
+
+var x = new Complex128Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );
+var y = new Complex128Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );
+
+zswap( x.length, x, 1, y, 1 );
+
+var z = y.get( 0 );
+// returns <Complex128>
+
+var re = real( z );
+// returns 1.0
+
+var im = imag( z );
+// returns 2.0
+
+z = x.get( 0 );
+// returns <Complex128>
+
+re = real( z );
+// returns 0.0
+
+im = imag( z );
+// returns 0.0
+```
+
+The function has the following parameters:
+
+-   **N**: number of indexed elements.
+-   **x**: first input [`Complex128Array`][@stdlib/array/complex128].
+-   **strideX**: index increment for `x`.
+-   **y**: second input [`Complex128Array`][@stdlib/array/complex128].
+-   **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 Complex128Array = require( '@stdlib/array/complex128' );
+var real = require( '@stdlib/complex/real' );
+var imag = require( '@stdlib/complex/imag' );
+
+var x = new Complex128Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0 ] );
+var y = new Complex128Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );
+
+zswap( 2, x, -2, y, 1 );
+
+var z = y.get( 0 );
+// returns <Complex128>
+
+var re = real( z );
+// returns 5.0
+
+var im = imag( z );
+// returns 6.0
+
+z = x.get( 0 );
+// returns <Complex128>
+
+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 Complex128Array = require( '@stdlib/array/complex128' );
+var real = require( '@stdlib/complex/real' );
+var imag = require( '@stdlib/complex/imag' );
+
+// Initial arrays...
+var x0 = new Complex128Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0 ] );
+var y0 = new Complex128Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );
+
+// Create offset views...
+var x1 = new Complex128Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
+var y1 = new Complex128Array( y0.buffer, y0.BYTES_PER_ELEMENT*2 ); // start at 3rd element
+
+// Interchange in reverse order every other value from `x1` into `y1`...
+zswap( 2, x1, -2, y1, 1 );
+
+var z = y0.get( 2 );
+// returns <Complex128>
+
+var re = real( z );
+// returns 7.0
+
+var im = imag( z );
+// returns 8.0
+
+z = x0.get( 1 );
+// returns <Complex128>
+
+re = real( z );
+// returns 0.0
+
+im = imag( z );
+// returns 0.0
+```
+
+#### zswap.ndarray( N, x, strideX, offsetX, y, strideY, offsetY )
+
+Interchange two complex double-precision floating-point vectors using alternative indexing semantics.
+
+```javascript
+var Complex128Array = require( '@stdlib/array/complex128' );
+var real = require( '@stdlib/complex/real' );
+var imag = require( '@stdlib/complex/imag' );
+
+var x = new Complex128Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );
+var y = new Complex128Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );
+
+zswap.ndarray( x.length, x, 1, 0, y, 1, 0 );
+
+var z = y.get( 0 );
+// returns <Complex128>
+
+var re = real( z );
+// returns 1.0
+
+var im = imag( z );
+// returns 2.0
+
+z = x.get( 0 );
+// returns <Complex128>
+
+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 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 ]`, and so on.
+
+```javascript
+var Complex128Array = require( '@stdlib/array/complex128' );
+var real = require( '@stdlib/complex/real' );
+var imag = require( '@stdlib/complex/imag' );
+
+var x = new Complex128Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0 ] );
+var y = new Complex128Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );
+
+zswap.ndarray( 2, x, 2, 1, y, -1, y.length-1 );
+
+var z = y.get( y.length-1 );
+// returns <Complex128>
+
+var re = real( z );
+// returns 3.0
+
+var im = imag( z );
+// returns 4.0
+
+z = x.get( x.length-1 );
+// returns <Complex128>
+
+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.
+-   `zswap()` corresponds to the [BLAS][blas] level 1 function [`zswap`][zswap].
+
+</section>
+
+<!-- /.notes -->
+
+<section class="examples">
+
+## Examples
+
+<!-- eslint no-undef: "error" -->
+
+```javascript
+var discreteUniform = require( '@stdlib/random/base/discrete-uniform' );
+var filledarrayBy = require( '@stdlib/array/filled-by' );
+var Complex128 = require( '@stdlib/complex/float64' );
+var zswap = require( '@stdlib/blas/base/zswap' );
+
+function rand() {
+    return new Complex128( discreteUniform( 0, 10 ), discreteUniform( -5, 5 ) );
+}
+
+var x = filledarrayBy( 10, 'complex128', rand );
+console.log( x.get( 0 ).toString() );
+
+var y = filledarrayBy( 10, 'complex128', rand );
+console.log( y.get( 0 ).toString() );
+
+// Swap elements in `x` into `y` starting from the end of `y`:
+zswap( 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 for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->
+
+<section class="related">
+
+</section>
+
+<!-- /.related -->
+
+<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
+
+<section class="links">
+
+[blas]: http://www.netlib.org/blas
+
+[zswap]: https://netlib.org/lapack/explore-html-3.6.1/d2/df9/group__complex16__blas__level1_ga13a187010a0cae1fef2820072404e857.html#ga13a187010a0cae1fef2820072404e857
+
+[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray
+
+[@stdlib/array/complex128]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/array/complex128
+
+</section>
+
+<!-- /.links -->