npm package: @stdlib/blas-base-zdscal
Description: Scale a double-precision complex floating-point vector by a double-precision floating-point constant.
Author: The Stdlib Authors
Latest version: 0.1.1

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# zdscal

[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url] <!-- [![dependencies][dependencies-image]][dependencies-url] -->

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

<section class="installation">

## Installation

```bash
npm install @stdlib/blas-base-zdscal
```

</section>

<section class="usage">

## Usage

```javascript
var zdscal = require( '@stdlib/blas-base-zdscal' );
```

#### zdscal( N, alpha, x, strideX )

Scales a double-precision complex floating-point vector by a double-precision floating-point constant.

```javascript
var Complex128Array = require( '@stdlib/array-complex128' );

var x = new Complex128Array( [ 1.0, 1.0, 1.0, 1.0, 1.0, 1.0 ] );

zdscal( 3, 2.0, x, 1 );
// x => <Complex128Array>[ 2.0, 2.0, 2.0, 2.0, 2.0, 2.0 ]
```

The function has the following parameters:

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

The `N` and stride parameters determine which elements in `x` are scaled by `alpha`. For example, to scale every other element in `x` by `alpha`,

```javascript
var Complex128Array = require( '@stdlib/array-complex128' );

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

zdscal( 2, 2.0, x, 2 );
// x => <Complex128Array>[ 2.0, 4.0, 3.0, 4.0, 10.0, 12.0, 7.0, 8.0 ]
```

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' );

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

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

// Scale every element in `x1`:
zdscal( 3, 2.0, x1, 1 );
// x0 => <Complex128Array>[ 1.0, 2.0, 6.0, 8.0, 10.0, 12.0, 14.0, 16.0 ]
```

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

Scales a double-precision complex floating-point vector by a double-precision floating-point constant using alternative indexing semantics.

```javascript
var Complex128Array = require( '@stdlib/array-complex128' );

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

zdscal.ndarray( 3, 2.0, x, 1, 0 );
// x => <Complex128Array>[ 2.0, 4.0, 6.0, 8.0, 10.0, 12.0 ]
```

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 element in the input strided array starting from the second element,

```javascript
var Complex128Array = require( '@stdlib/array-complex128' );

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

zdscal.ndarray( 2, 2.0, x, 2, 1 );
// x => <Complex128Array>[ 1.0, 2.0, 6.0, 8.0, 5.0, 6.0, 14.0, 16.0 ]
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

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

</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-ctor' );
var zdscal = require( '@stdlib/blas-base-zdscal' );

function rand() {
    return new Complex128( discreteUniform( 0, 10 ), discreteUniform( -5, 5 ) );
}

var x = filledarrayBy( 10, 'complex128', rand );
console.log( x.toString() );

zdscal( x.length, 2.0, x, 1 );
console.log( x.toString() );
```

</section>

<!-- /.examples -->

<!-- C interface documentation. -->

* * *

<section class="c">

## C APIs

<!-- Section to include introductory text. Make sure to keep an empty line after the intro `section` element and another before the `/section` close. -->

<section class="intro">

</section>

<!-- /.intro -->

<!-- C usage documentation. -->

<section class="usage">

### Usage

```c
#include "stdlib/blas/base/zdscal.h"
```

#### c_zdscal( N, alpha, \*X, strideX )

Scales a double-precision complex floating-point vector by a double-precision floating-point constant.

```c
#include "stdlib/complex/float64/ctor.h"

stdlib_complex128_t x[] = {
    stdlib_complex128( 1.0, 2.0 ),
    stdlib_complex128( 3.0, 4.0 ),
    stdlib_complex128( 5.0, 6.0 )
};

c_zdscal( 3, 2.0, x, 1 );
```

The function accepts the following arguments:

-   **N**: `[in] CBLAS_INT` number of indexed elements.
-   **alpha**: `[in] double` scalar constant.
-   **X**: `[inout] stdlib_complex128_t*` input array.
-   **strideX**: `[in] CBLAS_INT` index increment for `x`.

```c
void c_zdscal( const CBLAS_INT N, const double alpha, void *X, const CBLAS_INT strideX );
```

#### c_zdscal_ndarray( N, alpha, \*X, strideX, offsetX )

Scales a double-precision complex floating-point vector by a double-precision floating-point constant using alternative indexing semantics.

```c
#include "stdlib/complex/float64/ctor.h"

stdlib_complex128_t x[] = {
    stdlib_complex128( 1.0, 2.0 ),
    stdlib_complex128( 3.0, 4.0 ),
    stdlib_complex128( 5.0, 6.0 )
};

c_zdscal_ndarray( 3, 2.0, x, 1, 0 );
```

The function accepts the following arguments:

-   **N**: `[in] CBLAS_INT` number of indexed elements.
-   **alpha**: `[in] double` scalar constant.
-   **X**: `[inout] void*` input array.
-   **strideX**: `[in] CBLAS_INT` index increment for `x`.
-   **offsetX**: `[in] CBLAS_INT` starting index for `x`.

```c
void c_zdscal_ndarray( const CBLAS_INT N, const double alpha, void *X, const CBLAS_INT strideX, const CBLAS_INT offsetX );
```

</section>

<!-- /.usage -->

<!-- C API usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="notes">

</section>

<!-- /.notes -->

<!-- C API usage examples. -->

<section class="examples">

### Examples

```c
#include "stdlib/blas/base/zdscal.h"
#include "stdlib/complex/float64/ctor.h"
#include "stdlib/complex/float64/real.h"
#include "stdlib/complex/float64/imag.h"
#include <stdio.h>

int main( void ) {
    stdlib_complex128_t x[] = {
        stdlib_complex128( 1.0, 2.0 ),
        stdlib_complex128( 3.0, 4.0 ),
        stdlib_complex128( 5.0, 6.0 ),
        stdlib_complex128( 7.0, 8.0 )
    };

    // Specify the number of elements:
    const int N = 4;

    // Specify the stride length:
    const int strideX = 1;

    c_zdscal( N, 2.0, (void *)x, strideX );

    // Print the result:
    for ( int i = 0; i < N; i++ ) {
        printf( "x[ %i ] = %lf + %lfj\n", i, stdlib_complex128_real( x[ i ] ), stdlib_complex128_imag( x[ i ] ) );
    }

    c_zdscal_ndarray( N, 2.0, (void *)x, strideX, 0 );

    // Print the result:
    for ( int i = 0; i < N; i++ ) {
        printf( "x[ %i ] = %lf + %lfj\n", i, stdlib_complex128_real( x[ i ] ), stdlib_complex128_imag( x[ i ] ) );
    }
}
```

</section>

<!-- /.examples -->

</section>

<!-- /.c -->

<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->

<section class="related">

</section>

<!-- /.related -->

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<section class="main-repo" >

* * *

## Notice

This package is part of [stdlib][stdlib], a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

For more information on the project, filing bug reports and feature requests, and guidance on how to develop [stdlib][stdlib], see the main project [repository][stdlib].

#### Community

[![Chat][chat-image]][chat-url]

---

## License

See [LICENSE][stdlib-license].


## Copyright

Copyright &copy; 2016-2026. The Stdlib [Authors][stdlib-authors].

</section>

<!-- /.stdlib -->

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<section class="links">

[npm-image]: http://img.shields.io/npm/v/@stdlib/blas-base-zdscal.svg
[npm-url]: https://npmjs.org/package/@stdlib/blas-base-zdscal

[test-image]: https://github.com/stdlib-js/blas-base-zdscal/actions/workflows/test.yml/badge.svg?branch=v0.1.1
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[umd]: https://github.com/umdjs/umd
[es-module]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules

[deno-url]: https://github.com/stdlib-js/blas-base-zdscal/tree/deno
[deno-readme]: https://github.com/stdlib-js/blas-base-zdscal/blob/deno/README.md
[umd-url]: https://github.com/stdlib-js/blas-base-zdscal/tree/umd
[umd-readme]: https://github.com/stdlib-js/blas-base-zdscal/blob/umd/README.md
[esm-url]: https://github.com/stdlib-js/blas-base-zdscal/tree/esm
[esm-readme]: https://github.com/stdlib-js/blas-base-zdscal/blob/esm/README.md
[branches-url]: https://github.com/stdlib-js/blas-base-zdscal/blob/main/branches.md

[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/blas-base-zdscal/main/LICENSE

[blas]: http://www.netlib.org/blas

[zdscal]: https://www.netlib.org/lapack/explore-html/d2/de8/group__scal_ga40d50a435a5fcf16cf41fa80d746819f.html#ga40d50a435a5fcf16cf41fa80d746819f

[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

</section>

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