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# zdscal

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

<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 -->

<!-- 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

[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>

<!-- /.links -->
