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# zcopy

> Copy values from one double-precision complex floating-point vector to another double-precision complex floating-point vector.

<section class="usage">

## Usage

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

#### zcopy( N, x, strideX, y, strideY )

Copies values from `x` into `y`.

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

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 ] );

zcopy( x.length, x, 1, y, 1 );
// y => <Complex128Array>[ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ]
```

The function has the following parameters:

-   **N**: number of indexed elements.
-   **x**: input [`Complex128Array`][@stdlib/array/complex128].
-   **strideX**: index increment for `x`.
-   **y**: destination [`Complex128Array`][@stdlib/array/complex128].
-   **strideY**: index increment for `y`.

The `N` and stride parameters determine how values from `x` are copied into `y`. For example, to copy in reverse order every other value in `x` into the first `N` elements of `y`,

```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 ] );
var y = new Complex128Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );

zcopy( 2, x, -2, y, 1 );
// y => <Complex128Array>[ 5.0, 6.0, 1.0, 2.0, 0.0, 0.0, 0.0, 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' );

// 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

// Copy in reverse order every other value from `x1` into `y1`...
zcopy( 2, x1, -2, y1, 1 );
// y0 => <Complex128Array>[ 0.0, 0.0, 0.0, 0.0, 7.0, 8.0, 3.0, 4.0 ]
```

#### zcopy.ndarray( N, x, strideX, offsetX, y, strideY, offsetY )

Copies values from `x` into `y` 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 ] );
var y = new Complex128Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );

zcopy.ndarray( x.length, x, 1, 0, y, 1, 0 );
// y => <Complex128Array>[ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ]
```

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 copy 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]`,...,

```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 ] );
var y = new Complex128Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );

zcopy.ndarray( 2, x, 2, 1, y, -1, y.length-1 );
// y => <Complex128Array>[ 0.0, 0.0, 0.0, 0.0, 7.0, 8.0, 3.0, 4.0 ]
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

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

</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 zcopy = require( '@stdlib/blas/base/zcopy' );

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() );

// Copy elements from `x` into `y` starting from the end of `y`:
zcopy( x.length, x, 1, y, -1 );
console.log( y.get( y.length-1 ).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/zcopy.h"
```

#### c_zcopy( N, \*X, strideX, \*Y, strideY )

Copies values from `X` into `Y`.

```c
const double x[] = { 1.0, 2.0, 3.0, 4.0 }; // interleaved real and imaginary components
double y[] = { 0.0, 0.0, 0.0, 0.0 };

c_zcopy( 2, (void *)x, 1, (void *)y, 1 );
```

The function accepts the following arguments:

-   **N**: `[in] CBLAS_INT` number of indexed elements.
-   **X**: `[in] void*` input array.
-   **strideX**: `[in] CBLAS_INT` index increment for `X`.
-   **Y**: `[out] void*` output array.
-   **strideY**: `[in] CBLAS_INT` index increment for `Y`.

```c
void c_zcopy( const CBLAS_INT N, const void *X, const CBLAS_INT strideX, void *Y, const CBLAS_INT strideY );
```

#### c_zcopy_ndarray( N, \*X, strideX, offsetX, \*Y, strideY, offsetY )

Copies values from `X` into `Y` using alternative indexing semantics.

```c
const double x[] = { 1.0, 2.0, 3.0, 4.0 }; // interleaved real and imaginary components
double y[] = { 0.0, 0.0, 0.0, 0.0 };

c_zcopy_ndarray( 2, (void *)x, 1, 0, (void *)y, 1, 0 );
```

The function accepts the following arguments:

-   **N**: `[in] CBLAS_INT` number of indexed elements.
-   **X**: `[in] void*` input array.
-   **strideX**: `[in] CBLAS_INT` index increment for `X`.
-   **offsetX**: `[in] CBLAS_INT` starting index for `X`.
-   **Y**: `[out] void*` output array.
-   **strideY**: `[in] CBLAS_INT` index increment for `Y`.
-   **offsetY**: `[in] CBLAS_INT` starting index for `Y`.

```c
void c_zcopy_ndarray( const CBLAS_INT N, const void *X, const CBLAS_INT strideX, const CBLAS_INT offsetX, void *Y, const CBLAS_INT strideY, const CBLAS_INT offsetY );
```

</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/zcopy.h"
#include <stdio.h>

int main( void ) {
    // Create strided arrays:
    const double x[] = { 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0 };
    double y[] = { 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 };

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

    // Specify stride lengths:
    const int strideX = 1;
    const int strideY = -1;

    // Copy elements:
    c_zcopy( N, (void *)x, strideX, (void *)y, strideY );

    // Print the result:
    for ( int i = 0; i < N; i++ ) {
        printf( "y[ %i ] = %lf + %lfj\n", i, y[ i*2 ], y[ (i*2)+1 ] );
    }

    // Copy elements using alternative indexing semantics:
    c_zcopy_ndarray( N, (void *)x, -strideX, N-1, (void *)y, strideY, N-1 );

    // Print the result:
    for ( int i = 0; i < N; i++ ) {
        printf( "y[ %i ] = %lf + %lfj\n", i, y[ i*2 ], y[ (i*2)+1 ] );
    }
}
```

</section>

<!-- /.examples -->

</section>

<!-- /.c -->

<!-- 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

[zcopy]: https://www.netlib.org/lapack/explore-html/d5/d2b/group__copy_gaca1a115319081adeb0a9b80ec37ce626.html#gaca1a115319081adeb0a9b80ec37ce626

[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 -->
