# scnrm2
> Compute the L2-norm of a complex single-precision floating-point vector.
## Usage
```javascript
var scnrm2 = require( '@stdlib/blas/base/scnrm2' );
```
#### scnrm2( N, cx, strideX )
Computes the L2-norm of a complex single-precision floating-point vector.
```javascript
var Complex64Array = require( '@stdlib/array/complex64' );
var cx = new Complex64Array( [ 0.3, 0.1, 0.5, 0.0, 0.0, 0.5, 0.0, 0.2 ] );
var norm = scnrm2( 4, cx, 1 );
// returns ~0.8
```
The function has the following parameters:
- **N**: number of indexed elements.
- **cx**: input [`Complex64Array`][@stdlib/array/complex64].
- **strideX**: index increment for `cx`.
The `N` and stride parameters determine which elements in the strided array are accessed at runtime. For example, to traverse every other value,
```javascript
var Complex64Array = require( '@stdlib/array/complex64' );
var cx = new Complex64Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
var norm = scnrm2( 2, cx, 2 );
// returns ~4.6
```
Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][mdn-typed-array] views.
```javascript
var Complex64Array = require( '@stdlib/array/complex64' );
// Initial array:
var cx0 = new Complex64Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );
// Create an offset view:
var cx1 = new Complex64Array( cx0.buffer, cx0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
// Compute the L2-norm:
var norm = scnrm2( 2, cx1, 1 );
// returns ~9.3
```
#### scnrm2.ndarray( N, cx, strideX, offset )
Computes the L2-norm of a complex single-precision floating-point vector using alternative indexing semantics.
```javascript
var Complex64Array = require( '@stdlib/array/complex64' );
var cx = new Complex64Array( [ 0.3, 0.1, 0.5, 0.0, 0.0, 0.5, 0.0, 0.2 ] );
var norm = scnrm2.ndarray( 4, cx, 1, 0 );
// returns ~0.8
```
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 start from the second index,
```javascript
var Complex64Array = require( '@stdlib/array/complex64' );
var cx = new Complex64Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );
var norm = scnrm2.ndarray( 2, cx, 1, 1 );
// returns ~9.3
```
## Notes
- If `N <= 0`, both functions return `0.0`.
- `scnrm2()` corresponds to the [BLAS][blas] level 1 function [`scnrm2`][scnrm2].
## Examples
```javascript
var discreteUniform = require( '@stdlib/random/base/discrete-uniform' );
var filledarrayBy = require( '@stdlib/array/filled-by' );
var Complex64 = require( '@stdlib/complex/float32/ctor' );
var scnrm2 = require( '@stdlib/blas/base/scnrm2' );
function rand() {
return new Complex64( discreteUniform( 0, 10 ), discreteUniform( -5, 5 ) );
}
var cx = filledarrayBy( 10, 'complex64', rand );
console.log( cx.toString() );
// Compute the L2-norm:
var norm = scnrm2( cx.length, cx, 1 );
console.log( norm );
```
* * *
## C APIs
### Usage
```c
#include "stdlib/blas/base/scnrm2.h"
```
#### c_scnrm2( N, \*CX, strideX )
Computes the L2-norm of a complex single-precision floating-point vector.
```c
const float cx[] = { 0.3f, 0.1f, 0.5f, 0.0f, 0.0f, 0.5f, 0.0f, 0.2f };
float norm = c_scnrm2( 4, (void *)cx, 1 );
// returns 0.8
```
The function accepts the following arguments:
- **N**: `[in] CBLAS_INT` number of indexed elements.
- **CX**: `[in] void*` input array.
- **strideX**: `[in] CBLAS_INT` index increment for `CX`.
```c
float c_scnrm2( const CBLAS_INT N, const void *CX, const CBLAS_INT strideX );
```
### Examples
```c
#include "stdlib/blas/base/scnrm2.h"
#include
int main( void ) {
// Create a strided array of interleaved real and imaginary components:
const float cx[] = { 1.0f, 2.0f, 3.0f, 4.0f, 5.0f, 6.0f, 7.0f, 8.0f };
// Specify the number of elements:
const int N = 4;
// Specify stride length:
const int strideX = 1;
// Compute the L2-norm:
c_scnrm2( N, (void *)cx, strideX );
// Print the result:
printf( "L2-norm: %f\n", norm );
}
```
[blas]: http://www.netlib.org/blas
[scnrm2]: https://www.netlib.org/lapack/explore-html/d1/d2a/group__nrm2_gaee5779d5d216a7cd8cf83488fb6bb175.html#gaee5779d5d216a7cd8cf83488fb6bb175
[@stdlib/array/complex64]: https://www.npmjs.com/package/@stdlib/array-complex64
[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray