# sapx
> Add a constant to each element in a single-precision floating-point strided array.
## Usage
```javascript
var sapx = require( '@stdlib/blas/ext/base/sapx' );
```
#### sapx( N, alpha, x, stride )
Adds a constant `alpha` to each element in a single-precision floating-point strided array `x`.
```javascript
var Float32Array = require( '@stdlib/array/float32' );
var x = new Float32Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
sapx( x.length, 5.0, x, 1 );
// x => [ 3.0, 6.0, 8.0, 0.0, 9.0, 5.0, 4.0, 2.0 ]
```
The function has the following parameters:
- **N**: number of indexed elements.
- **alpha**: scalar constant.
- **x**: input [`Float32Array`][@stdlib/array/float32].
- **stride**: index increment.
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 Float32Array = require( '@stdlib/array/float32' );
var x = new Float32Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
sapx( 4, 5.0, x, 2 );
// x => [ 3.0, 1.0, 8.0, -5.0, 9.0, 0.0, 4.0, -3.0 ]
```
Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][mdn-typed-array] views.
```javascript
var Float32Array = require( '@stdlib/array/float32' );
// Initial array...
var x0 = new Float32Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );
// Create an offset view...
var x1 = new Float32Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
// Add a constant to every other element...
sapx( 3, 5.0, x1, 2 );
// x0 => [ 1.0, 3.0, 3.0, 1.0, 5.0, -1.0 ]
```
#### sapx.ndarray( N, alpha, x, stride, offset )
Adds a constant `alpha` to each element in a single-precision floating-point strided array `x` using alternative indexing semantics.
```javascript
var Float32Array = require( '@stdlib/array/float32' );
var x = new Float32Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
sapx.ndarray( x.length, 5.0, x, 1, 0 );
// x => [ 3.0, 6.0, 8.0, 0.0, 9.0, 5.0, 4.0, 2.0 ]
```
The function has the following additional parameters:
- **offset**: 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 three elements of the strided array
```javascript
var Float32Array = require( '@stdlib/array/float32' );
var x = new Float32Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );
sapx.ndarray( 3, 5.0, x, 1, x.length-3 );
// x => [ 1.0, -2.0, 3.0, 1.0, 10.0, -1.0 ]
```
## Notes
- If `N <= 0`, both functions return the input array unchanged.
## Examples
```javascript
var uniform = require( '@stdlib/random/base/uniform' ).factory;
var filledarrayBy = require( '@stdlib/array/filled-by' );
var sapx = require( '@stdlib/blas/ext/base/sapx' );
var x = filledarrayBy( 10, 'float32', uniform( -100.0, 100.0 ) );
console.log( x );
sapx( x.length, 5.0, x, 1 );
console.log( x );
```
[@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/ext/base/dapx]: https://github.com/stdlib-js/blas/tree/main/ext/base/dapx
[@stdlib/blas/ext/base/gapx]: https://github.com/stdlib-js/blas/tree/main/ext/base/gapx