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# zscal

> Scale a double-precision complex floating-point vector by a double-precision complex floating-point constant.

<section class="usage">

## Usage

```javascript
var zscal = require( '@stdlib/blas/base/wasm/zscal' );
```

#### zscal.main( N, alpha, x, strideX )

Scales values from `x` by `alpha`.

```javascript
var Complex128Array = require( '@stdlib/array/complex128' );
var Complex128 = require( '@stdlib/complex/float64/ctor' );

// Define a strided array:
var x = new Complex128Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );

// Define a scalar constant:
var alpha = new Complex128( 2.0, 2.0 );

// Perform operation:
zscal.main( x.length, alpha, x, 1 );
// x => <Complex128Array>[ -2.0, 6.0, -2.0, 14.0, -2.0, 22.0 ]
```

The function has the following parameters:

-   **N**: number of indexed elements.
-   **alpha**: scalar [`Complex128`][@stdlib/complex/float64/ctor] constant.
-   **x**: input [`Complex128Array`][@stdlib/array/complex128].
-   **strideX**: stride length for `x`.

The `N` and stride parameters determine which elements in the input strided array are accessed at runtime. For example, to scale every other value in `x` by `alpha`,

```javascript
var Complex128Array = require( '@stdlib/array/complex128' );
var Complex128 = require( '@stdlib/complex/float64/ctor' );

// Define a strided array:
var x = new Complex128Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );

// Define a scalar constant:
var alpha = new Complex128( 2.0, 2.0 );

// Perform operation:
zscal.main( 2, alpha, x, 2 );
// x => <Complex128Array>[ -2.0, 6.0, 3.0, 4.0, -2.0, 22.0 ]
```

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 Complex128 = require( '@stdlib/complex/float64/ctor' );

// Initial array:
var x0 = new Complex128Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0 ] );

// Define a scalar constant:
var alpha = new Complex128( 2.0, 2.0 );

// Create an offset view:
var x1 = new Complex128Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element

// Scales every other value from `x1` by `alpha`...
zscal.main( 3, alpha, x1, 1 );
// x0 => <Complex128Array>[ 1.0, 2.0, -2.0, 14.0, -2.0, 22.0, -2.0, 30.0 ]
```

#### zscal.ndarray( N, alpha, x, strideX, offsetX )

Scales values from `x` by `alpha` using alternative indexing semantics.

```javascript
var Complex128Array = require( '@stdlib/array/complex128' );
var Complex128 = require( '@stdlib/complex/float64/ctor' );

// Define a strided array:
var x = new Complex128Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );

// Define a scalar constant:
var alpha = new Complex128( 2.0, 2.0 );

// Perform operation:
zscal.ndarray( x.length, alpha, x, 1, 0 );
// x => <Complex128Array>[ -2.0, 6.0, -2.0, 14.0, -2.0, 22.0 ]
```

The function has the following additional parameters:

-   **offsetX**: starting index for `x`.

While [`typed array`][mdn-typed-array] views mandate a view offset based on the underlying buffer, the offset parameter supports indexing semantics based on a starting index. For example, to scale every other value in the input strided array starting from the second element,

```javascript
var Complex128Array = require( '@stdlib/array/complex128' );
var Complex128 = require( '@stdlib/complex/float64/ctor' );

var x = new Complex128Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0 ] );
var alpha = new Complex128( 2.0, 2.0 );

zscal.ndarray( 2, alpha, x, 2, 1 );
// x => <Complex128Array>[ 1.0, 2.0, -2.0, 14.0, 5.0, 6.0, -2.0, 30.0 ]
```

* * *

### Module

#### zscal.Module( memory )

Returns a new WebAssembly [module wrapper][@stdlib/wasm/module-wrapper] instance which uses the provided WebAssembly [memory][@stdlib/wasm/memory] instance as its underlying memory.

<!-- eslint-disable n/no-sync -->

```javascript
var Memory = require( '@stdlib/wasm/memory' );

// Create a new memory instance with an initial size of 10 pages (640KiB) and a maximum size of 100 pages (6.4MiB):
var mem = new Memory({
    'initial': 10,
    'maximum': 100
});

// Create a BLAS routine:
var mod = new zscal.Module( mem );
// returns <Module>

// Initialize the routine:
mod.initializeSync();
```

#### zscal.Module.prototype.main( N, ap, xp, sx )

Scales values from `x` by `alpha`.

<!-- eslint-disable n/no-sync -->

```javascript
var Memory = require( '@stdlib/wasm/memory' );
var oneTo = require( '@stdlib/array/one-to' );
var ones = require( '@stdlib/array/ones' );
var zeros = require( '@stdlib/array/zeros' );
var bytesPerElement = require( '@stdlib/ndarray/base/bytes-per-element' );
var Float64Array = require( '@stdlib/array/float64' );
var Complex128Array = require( '@stdlib/array/complex128' );
var reinterpretComplex128 = require( '@stdlib/strided/base/reinterpret-complex128' );
var zscal = require( '@stdlib/blas/base/wasm/zscal' );

// Create a new memory instance with an initial size of 10 pages (320KiB) and a maximum size of 100 pages (6.4MiB):
var mem = new Memory({
    'initial': 10,
    'maximum': 100
});

// Create a BLAS routine:
var mod = new zscal.Module( mem );
// returns <Module>

// Initialize the routine:
mod.initializeSync();

// Define a vector data type:
var dtype = 'complex128';

// Specify a vector length:
var N = 5;

// Define a pointer (i.e., byte offset) for storing the input vector:
var xptr = 0;

// Define a pointer for storing a complex number:
var zptr = N * bytesPerElement( dtype );

// Write vector values to module memory:
var xbuf = oneTo( N*2, 'float64' );
var x = new Complex128Array( xbuf.buffer );
mod.write( xptr, x );

// Write a complex number to module memory:
mod.write( zptr, new Float64Array( [ 2.0, 2.0 ] ) );

// Perform computation:
mod.main( N, zptr, xptr, 1 );

// Read out the results:
var view = zeros( N, dtype );
mod.read( xptr, view );

console.log( reinterpretComplex128( view, 0 ) );
// => <Float64Array>[ -2.0, 6.0, -2.0, 14.0, -2.0, 22.0, -2.0, 30.0, -2.0, 38.0 ]
```

The function has the following parameters:

-   **N**: number of indexed elements.
-   **ap**: pointer (i.e., byte offset) to a scalar [`Complex128`][@stdlib/complex/float64/ctor] constant.
-   **xp**: input [`Complex128Array`][@stdlib/array/complex128] pointer (i.e., byte offset).
-   **sx**: stride length for `x`.

#### zscal.Module.prototype.ndarray( N, ap, xp, sx, ox )

Scales values from `x` by `alpha`  using alternative indexing semantics.

<!-- eslint-disable n/no-sync -->

```javascript
var Memory = require( '@stdlib/wasm/memory' );
var oneTo = require( '@stdlib/array/one-to' );
var ones = require( '@stdlib/array/ones' );
var zeros = require( '@stdlib/array/zeros' );
var bytesPerElement = require( '@stdlib/ndarray/base/bytes-per-element' );
var Float64Array = require( '@stdlib/array/float64' );
var Complex128Array = require( '@stdlib/array/complex128' );
var reinterpretComplex128 = require( '@stdlib/strided/base/reinterpret-complex128' );
var zscal = require( '@stdlib/blas/base/wasm/zscal' );

// Create a new memory instance with an initial size of 10 pages (320KiB) and a maximum size of 100 pages (6.4MiB):
var mem = new Memory({
    'initial': 10,
    'maximum': 100
});

// Create a BLAS routine:
var mod = new zscal.Module( mem );
// returns <Module>

// Initialize the routine:
mod.initializeSync();

// Define a vector data type:
var dtype = 'complex128';

// Specify a vector length:
var N = 5;

// Define a pointer (i.e., byte offset) for storing the input vector:
var xptr = 0;

// Define a pointer for storing a complex number:
var zptr = N * bytesPerElement( dtype );

// Write vector values to module memory:
var xbuf = oneTo( N*2, 'float64' );
var x = new Complex128Array( xbuf.buffer );
mod.write( xptr, x );

// Write a complex number to module memory:
mod.write( zptr, new Float64Array( [ 2.0, 2.0 ] ) );

// Perform computation:
mod.ndarray( N, zptr, xptr, 1, 0 );

// Read out the results:
var view = zeros( N, dtype );
mod.read( xptr, view );

console.log( reinterpretComplex128( view, 0 ) );
// => <Float64Array>[ -2.0, 6.0, -2.0, 14.0, -2.0, 22.0, -2.0, 30.0, -2.0, 38.0 ]
```

The function has the following additional parameters:

-   **ox**: starting index for `x`.

</section>

<!-- /.usage -->

<section class="notes">

* * *

## Notes

-   If `N <= 0`, `x` is left unchanged.
-   This package implements routines using WebAssembly. When provided arrays which are not allocated on a `zscal` module memory instance, data must be explicitly copied to module memory prior to computation. Data movement may entail a performance cost, and, thus, if you are using arrays external to module memory, you should prefer using [`@stdlib/blas/base/zscal`][@stdlib/blas/base/zscal]. However, if working with arrays which are allocated and explicitly managed on module memory, you can achieve better performance when compared to the pure JavaScript implementations found in [`@stdlib/blas/base/zscal`][@stdlib/blas/base/zscal]. Beware that such performance gains may come at the cost of additional complexity when having to perform manual memory management. Choosing between implementations depends heavily on the particular needs and constraints of your application, with no one choice universally better than the other.
-   `zscal()` corresponds to the [BLAS][blas] level 1 function [`zscal`][zscal].

</section>

<!-- /.notes -->

<section class="examples">

* * *

## Examples

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

```javascript
var hasWebAssemblySupport = require( '@stdlib/assert/has-wasm-support' );
var oneTo = require( '@stdlib/array/one-to' );
var Complex128 = require( '@stdlib/complex/float64/ctor' );
var Complex128Array = require( '@stdlib/array/complex128' );
var reinterpretComplex128 = require( '@stdlib/strided/base/reinterpret-complex128' );
var zscal = require( '@stdlib/blas/base/wasm/zscal' );

// Specify a vector length:
var N = 5;

// Create an input array:
var xbuf = oneTo( N*2, 'float64' );
var x = new Complex128Array( xbuf.buffer );

// Create a complex number:
var alpha = new Complex128( 2.0, 2.0 );

// Perform computation:
zscal.ndarray( N, alpha, x, 1, 0 );

// Print the results:
console.log( reinterpretComplex128( x, 0 ) );
// => <Float64Array>[ -2.0, 6.0, -2.0, 14.0, -2.0, 22.0, -2.0, 30.0, -2.0, 38.0 ]
```

</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

[zscal]: 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/complex128]: https://www.npmjs.com/package/@stdlib/array-complex128

[@stdlib/complex/float64/ctor]: https://www.npmjs.com/package/@stdlib/complex-float64-ctor

[@stdlib/wasm/memory]: https://www.npmjs.com/package/@stdlib/wasm-memory

[@stdlib/wasm/module-wrapper]: https://www.npmjs.com/package/@stdlib/wasm-module-wrapper

[@stdlib/blas/base/zscal]: https://github.com/stdlib-js/blas/tree/main/base/zscal

</section>

<!-- /.links -->
