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# sxsa

> Subtract a scalar constant from each element in a single-precision floating-point strided array.

<section class="usage">

## Usage

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

#### sxsa( N, alpha, x, strideX )

Subtracts a scalar constant from each element in a single-precision floating-point strided array.

```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 ] );

sxsa( x.length, 5.0, x, 1 );
// x => <Float32Array>[ -7.0, -4.0, -2.0, -10.0, -1.0, -5.0, -6.0, -8.0 ]
```

The function has the following parameters:

-   **N**: number of indexed elements.
-   **alpha**: scalar constant.
-   **x**: input [`Float32Array`][@stdlib/array/float32].
-   **strideX**: stride length.

The `N` and stride parameters determine which elements in the strided array are accessed at runtime. For example, to subtract a constant from 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 ] );

sxsa( 4, 5.0, x, 2 );
// x => <Float32Array>[ -7.0, 1.0, -2.0, -5.0, -1.0, 0.0, -6.0, -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

// Subtract a constant from every other element...
sxsa( 3, 5.0, x1, 2 );
// x0 => <Float32Array>[ 1.0, -7.0, 3.0, -9.0, 5.0, -11.0 ]
```

#### sxsa.ndarray( N, alpha, x, strideX, offsetX )

Subtracts a scalar constant from each element in a single-precision floating-point strided array 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 ] );

sxsa.ndarray( x.length, 5.0, x, 1, 0 );
// x => <Float32Array>[ -7.0, -4.0, -2.0, -10.0, -1.0, -5.0, -6.0, -8.0 ]
```

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 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 ] );

sxsa.ndarray( 3, 5.0, x, 1, x.length-3 );
// x => <Float32Array>[ 1.0, -2.0, 3.0, -9.0, 0.0, -11.0 ]
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

-   If `N <= 0`, both functions return the input array unchanged.

</section>

<!-- /.notes -->

<section class="examples">

## Examples

<!-- eslint no-undef: "error" -->

```javascript
var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
var sxsa = require( '@stdlib/blas/ext/base/sxsa' );

var x = discreteUniform( 10, -100, 100, {
    'dtype': 'float32'
});
console.log( x );

sxsa( x.length, 5.0, x, 1 );
console.log( x );
```

</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/ext/base/sxsa.h"
```

#### stdlib_strided_sxsa( N, alpha, \*X, strideX )

Subtracts a scalar constant from each element in a single-precision floating-point strided array.

```c
float x[] = { 1.0f, 2.0f, 3.0f, 4.0f };

stdlib_strided_sxsa( 4, 5.0f, x, 1 );
```

The function accepts the following arguments:

-   **N**: `[in] CBLAS_INT` number of indexed elements.
-   **alpha**: `[in] float` scalar constant.
-   **X**: `[inout] float*` input array.
-   **strideX**: `[in] CBLAS_INT` stride length.

```c
void stdlib_strided_sxsa( const CBLAS_INT N, const float alpha, float *X, const CBLAS_INT strideX );
```

#### stdlib_strided_sxsa_ndarray( N, alpha, \*X, strideX, offsetX )

Subtracts a scalar constant from each element in a single-precision floating-point strided array using alternative indexing semantics.

```c
float x[] = { 1.0f, 2.0f, 3.0f, 4.0f };

stdlib_strided_sxsa_ndarray( 4, 5.0f, x, 1, 0 );
```

The function accepts the following arguments:

-   **N**: `[in] CBLAS_INT` number of indexed elements.
-   **alpha**: `[in] float` scalar constant.
-   **X**: `[inout] float*` input array.
-   **strideX**: `[in] CBLAS_INT` stride length.
-   **offsetX**: `[in] CBLAS_INT` starting index.

```c
void stdlib_strided_sxsa_ndarray( const CBLAS_INT N, const float alpha, float *X, const CBLAS_INT strideX, const CBLAS_INT offsetX );
```

</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/ext/base/sxsa.h"
#include <stdio.h>

int main( void ) {
    // Create a strided array:
    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;

    // Subtract a constant from each element:
    stdlib_strided_sxsa( N, 5.0f, x, strideX );

    // Print the result:
    for ( int i = 0; i < 8; i++ ) {
        printf( "x[ %i ] = %f\n", i, x[ i ] );
    }
}
```

</section>

<!-- /.examples -->

</section>

<!-- /.c -->

<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->

<section class="related">

</section>

<!-- /.related -->

<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="links">

[@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

<!-- <related-links> -->

<!-- </related-links> -->

</section>

<!-- /.links -->
