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# zapx

> Add a scalar constant to each element in a double-precision complex floating-point strided array.

<section class="usage">

## Usage

```javascript
var zapx = require( '@stdlib/blas/ext/base/zapx' );
```

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

Adds a scalar constant to each element in a double-precision complex floating-point strided array.

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

var x = new Complex128Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );

var alpha = new Complex128( 5.0, 0.0 );

zapx( x.length, alpha, x, 1 );
// x => <Complex128Array>[ 3.0, 1.0, 8.0, -5.0, 9.0, 0.0, 4.0, -3.0 ]
```

The function has the following parameters:

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

The `N` and stride parameters determine which elements in the strided array are accessed at runtime. For example, to add a constant to every other element:

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

var x = new Complex128Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );

var alpha = new Complex128( 5.0, 0.0 );

zapx( 2, alpha, x, 2 );
// x => <Complex128Array>[ 3.0, 1.0, 3.0, -5.0, 9.0, 0.0, -1.0, -3.0 ]
```

Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][mdn-typed-array] views.

```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 ] );

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

// Define a scalar constant:
var alpha = new Complex128( 5.0, 0.0 );

// Add a constant to each element starting from the second element:
zapx( 2, alpha, x1, 1 );
// x0 => <Complex128Array>[ 1.0, -2.0, 8.0, -4.0, 10.0, -6.0 ]
```

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

Adds a scalar constant to each element in a double-precision complex floating-point strided array using alternative indexing semantics.

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

var x = new Complex128Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );

var alpha = new Complex128( 5.0, 0.0 );

zapx.ndarray( x.length, alpha, x, 1, 0 );
// x => <Complex128Array>[ 3.0, 1.0, 8.0, -5.0, 9.0, 0.0, 4.0, -3.0 ]
```

The function has the following additional parameters:

-   **offsetX**: starting index.

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 access only the last two elements of the strided array:

```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( 5.0, 0.0 );

zapx.ndarray( 2, alpha, x, 1, 2 );
// x => <Complex128Array>[ 1.0, -2.0, 3.0, -4.0, 10.0, -6.0, 12.0, -8.0 ]
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

-   If `N <= 0`, both functions return the strided array unchanged.

</section>

<!-- /.notes -->

<section class="examples">

## Examples

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

```javascript
var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
var Complex128Array = require( '@stdlib/array/complex128' );
var Complex128 = require( '@stdlib/complex/float64/ctor' );
var logEach = require( '@stdlib/console/log-each' );
var zapx = require( '@stdlib/blas/ext/base/zapx' );

var xbuf = discreteUniform( 20, -100, 100, {
    'dtype': 'float64'
});
var x = new Complex128Array( xbuf.buffer );
var alpha = new Complex128( 10.0, 10.0 );

zapx( x.length, alpha, x, 1 );
logEach( '%s', x );
```

</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/ext/base/zapx.h"
```

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

Adds a scalar constant to each element in a double-precision complex floating-point strided array.

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

double x[] = { 1.0, 2.0, 3.0, 4.0 };
const stdlib_complex128_t alpha = stdlib_complex128( 5.0, 0.0 );

stdlib_strided_zapx( 2, alpha, (stdlib_complex128_t *)x, 1 );
```

The function accepts the following arguments:

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

```c
void stdlib_strided_zapx( const CBLAS_INT N, const stdlib_complex128_t alpha, stdlib_complex128_t *X, const CBLAS_INT strideX );
```

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

Adds a scalar constant to each element in a double-precision complex floating-point strided array using alternative indexing semantics.

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

double x[] = { 1.0, 2.0, 3.0, 4.0 };
const stdlib_complex128_t alpha = stdlib_complex128( 5.0, 0.0 );

stdlib_strided_zapx_ndarray( 2, alpha, (stdlib_complex128_t *)x, 1, 0 );
```

The function accepts the following arguments:

-   **N**: `[in] CBLAS_INT` number of indexed elements.
-   **alpha**: `[in] stdlib_complex128_t` scalar constant.
-   **X**: `[inout] stdlib_complex128_t*` input array.
-   **strideX**: `[in] CBLAS_INT` stride length for `X`.
-   **offsetX**: `[in] CBLAS_INT` starting index for `X`.

```c
void stdlib_strided_zapx_ndarray( const CBLAS_INT N, const stdlib_complex128_t alpha, stdlib_complex128_t *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/ext/base/zapx.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 ) {
    // Create a strided array:
    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 indexed elements:
    const int N = 4;

    // Specify a stride:
    const int strideX = 1;

    // Scalar constant:
    stdlib_complex128_t alpha = stdlib_complex128( 5.0, 0.0 );

    // Add a constant to each element:
    stdlib_strided_zapx( N, alpha, x, strideX );

    // Print the result:
    for ( int i = 0; i < N; i++ ) {
        printf( "x[ %i ] = %lf + %lfi\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">

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

[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray

<!-- <related-links> -->

<!-- </related-links> -->

</section>

<!-- /.links -->
