# zcopy
> Copy values from one complex double-precision floating-point vector to another complex double-precision floating-point vector.
## 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 real = require( '@stdlib/complex/float64/real' );
var imag = require( '@stdlib/complex/float64/imag' );
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 );
var z = y.get( 0 );
// returns
var re = real( z );
// returns 1.0
var im = imag( z );
// returns 2.0
```
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 real = require( '@stdlib/complex/float64/real' );
var imag = require( '@stdlib/complex/float64/imag' );
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 );
var z = y.get( 0 );
// returns
var re = real( z );
// returns 5.0
var im = imag( z );
// returns 6.0
```
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 real = require( '@stdlib/complex/float64/real' );
var imag = require( '@stdlib/complex/float64/imag' );
// 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 );
var z = y0.get( 2 );
// returns
var re = real( z );
// returns 7.0
var im = imag( z );
// returns 8.0
```
#### 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 real = require( '@stdlib/complex/float64/real' );
var imag = require( '@stdlib/complex/float64/imag' );
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 );
var z = y.get( 0 );
// returns
var re = real( z );
// returns 1.0
var im = imag( z );
// returns 2.0
```
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 real = require( '@stdlib/complex/float64/real' );
var imag = require( '@stdlib/complex/float64/imag' );
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 );
var z = y.get( y.length-1 );
// returns
var re = real( z );
// returns 3.0
var im = imag( z );
// returns 4.0
```
## Notes
- If `N <= 0`, both functions return `y` unchanged.
- `zcopy()` corresponds to the [BLAS][blas] level 1 function [`zcopy`][zcopy].
## Examples
```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() );
```
[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