# snrm2
> Calculate the L2-norm of a single-precision floating-point vector.
The [L2-norm][l2-norm] is defined as
## Usage
```javascript
var snrm2 = require( '@stdlib/blas/base/snrm2' );
```
#### snrm2( N, x, stride )
Computes the [L2-norm][l2-norm] of a single-precision floating-point vector `x`.
```javascript
var Float32Array = require( '@stdlib/array/float32' );
var x = new Float32Array( [ 1.0, -2.0, 2.0 ] );
var z = snrm2( x.length, x, 1 );
// returns 3.0
```
The function has the following parameters:
- **N**: number of indexed elements.
- **x**: input [`Float32Array`][@stdlib/array/float32].
- **stride**: index increment for `x`.
The `N` and `stride` parameters determine which elements in the strided array are accessed at runtime. For example, to compute the [L2-norm][l2-norm] of every other element in `x`,
```javascript
var Float32Array = require( '@stdlib/array/float32' );
var x = new Float32Array( [ 1.0, 2.0, 2.0, -7.0, -2.0, 3.0, 4.0, 2.0 ] );
var z = snrm2( 4, x, 2 );
// returns 5.0
```
Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][mdn-typed-array] views.
```javascript
var Float32Array = require( '@stdlib/array/float32' );
var x0 = new Float32Array( [ 2.0, 1.0, 2.0, -2.0, -2.0, 2.0, 3.0, 4.0 ] );
var x1 = new Float32Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
var z = snrm2( 4, x1, 2 );
// returns 5.0
```
If `N` is less than or equal to `0`, the function returns `0`.
#### snrm2.ndarray( N, x, stride, offset )
Computes the [L2-norm][l2-norm] of a single-precision floating-point vector using alternative indexing semantics.
```javascript
var Float32Array = require( '@stdlib/array/float32' );
var x = new Float32Array( [ 1.0, -2.0, 2.0 ] );
var z = snrm2.ndarray( x.length, x, 1, 0 );
// returns 3.0
```
The function has the following additional parameters:
- **offset**: 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 calculate the [L2-norm][l2-norm] for every other value in `x` starting from the second value
```javascript
var Float32Array = require( '@stdlib/array/float32' );
var x = new Float32Array( [ 2.0, 1.0, 2.0, -2.0, -2.0, 2.0, 3.0, 4.0 ] );
var z = snrm2.ndarray( 4, x, 2, 1 );
// returns 5.0
```
## Notes
- If `N <= 0`, both functions return `0.0`.
- `snrm2()` corresponds to the [BLAS][blas] level 1 function [`snrm2`][snrm2].
## Examples
```javascript
var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
var snrm2 = require( '@stdlib/blas/base/snrm2' );
var opts = {
'dtype': 'float32'
};
var x = discreteUniform( 10, 0, 100, opts );
console.log( x );
var out = snrm2( x.length, x, 1 );
console.log( out );
```
* * *
## C APIs
### Usage
```c
#include "stdlib/blas/base/snrm2.h"
```
#### c_snrm2( N, \*X, stride )
Computes the L2-norm of a complex single-precision floating-point vector.
```c
const float x[] = { 1.0f, 2.0f, 2.0f, -7.0f, -2.0f, 3.0f, 4.0f, 2.0f };
float norm = c_snrm2( 4, x, 2 );
// returns 5.0f
```
The function accepts the following arguments:
- **N**: `[in] CBLAS_INT` number of indexed elements.
- **X**: `[in] float*` input array.
- **stride**: `[in] CBLAS_INT` index increment for `X`.
```c
float c_snrm2( const CBLAS_INT N, const float *X, const CBLAS_INT stride );
```
#### c_snrm2_ndarray( N, \*X, stride, offset )
Computes the L2-norm of a complex single-precision floating-point vector using alternative indexing semantics.
```c
const float x[] = { 1.0f, 2.0f, 2.0f, -7.0f, -2.0f, 3.0f, 4.0f, 2.0f };
float norm = c_snrm2_ndarray( 4, x, 2, 0 );
// returns 5.0f
```
The function accepts the following arguments:
- **N**: `[in] CBLAS_INT` number of indexed elements.
- **X**: `[in] float*` input array.
- **stride**: `[in] CBLAS_INT` index increment for `X`.
- **offset**: `[in] CBLAS_INT` starting index for `X`.
```c
float c_snrm2_ndarray( const CBLAS_INT N, const float *X, const CBLAS_INT stride, const CBLAS_INT offset );
```
### Examples
```c
#include "stdlib/blas/base/snrm2.h"
#include
int main( void ) {
// Create a strided array:
const float x[] = { 1.0f, -2.0f, 3.0f, -4.0f, 5.0f, -6.0f, 7.0f, -8.0f };
// Specify the number of indexed elements:
const int N = 8;
// Specify a stride:
const int strideX = 1;
// Compute the L2-norm:
float l2 = c_snrm2( N, x, strideX );
// Print the result:
printf( "L2-norm: %f\n", l2 );
// Compute the L2-norm:
l2 = c_snrm2_ndarray( N, x, -strideX, 7 );
// Print the result:
printf( "L2-norm: %f\n", l2 );
}
```
[l2-norm]: https://en.wikipedia.org/wiki/Euclidean_distance
[blas]: http://www.netlib.org/blas
[snrm2]: http://www.netlib.org/lapack/explore-html/df/d28/group__single__blas__level1.html
[@stdlib/array/float32]: https://www.npmjs.com/package/@stdlib/array-float32
[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray
[@stdlib/blas/base/dnrm2]: https://github.com/stdlib-js/blas/tree/main/base/dnrm2
[@stdlib/blas/base/gnrm2]: https://github.com/stdlib-js/blas/tree/main/base/gnrm2
