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# sscal

> Multiply a single-precision floating-point vector `x` by a constant `alpha`.

<section class="usage">

## Usage

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

#### sscal( N, alpha, x, stride )

Multiplies a single-precision floating-point vector `x` by a constant `alpha`.

```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 ] );

sscal( x.length, 5.0, x, 1 );
// x => <Float32Array>[ -10.0, 5.0, 15.0, -25.0, 20.0, 0.0, -5.0, -15.0 ]
```

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 `x` are accessed at runtime. For example, to multiply every other value by a constant

```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 ] );

sscal( 4, 5.0, x, 2 );
// x => <Float32Array>[ -10.0, 1.0, 15.0, -5.0, 20.0, 0.0, -5.0, -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

// Scale every other value:
sscal( 3, 5.0, x1, 2 );
// x0 => <Float32Array>[ 1.0, -10.0, 3.0, -20.0, 5.0, -30.0 ]
```

If either `N` or `stride` is less than or equal to `0`, the function returns `x` unchanged.

#### sscal.ndarray( N, alpha, x, stride, offset )

Multiplies a single-precision floating-point vector `x` by a constant `alpha` 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 ] );

sscal.ndarray( x.length, 5.0, x, 1, 0 );
// x => <Float32Array>[ -10.0, 5.0, 15.0, -25.0, 20.0, 0.0, -5.0, -15.0 ]
```

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 multiply the last three elements of `x` by a constant

```javascript
var Float32Array = require( '@stdlib/array/float32' );

var x = new Float32Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );

sscal.ndarray( 3, 5.0, x, 1, x.length-3 );
// x => <Float32Array>[ 1.0, -2.0, 3.0, -20.0, 25.0, -30.0 ]
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

-   If `N <= 0`, both functions return `x` unchanged.
-   `sscal()` corresponds to the [BLAS][blas] level 1 function [`sscal`][sscal].

</section>

<!-- /.notes -->

<section class="examples">

## Examples

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

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

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

sscal( 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/base/sscal.h"
```

#### c_sscal( N, alpha, \*X, stride )

Multiplies each element of a single-precision floating-point vector by a constant.

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

c_sscal( 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.
-   **stride**: `[in] CBLAS_INT` index increment for `X`.

```c
void c_sscal( const CBLAS_INT N, const float alpha, float *X, const CBLAS_INT stride );
```

#### c_sscal_ndarray( N, alpha, \*X, stride, offset )

Multiplies each element of a single-precision floating-point vector by a constant using alternative indexing semantics.

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

c_sscal_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.
-   **stride**: `[in] CBLAS_INT` index increment for `X`.
-   **offset**: `[in] CBLAS_INT` starting index for `X`.

```c
void c_sscal_ndarray( const CBLAS_INT N, const float alpha, float *X, const CBLAS_INT stride, const CBLAS_INT offset );
```

</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/base/sscal.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 elements:
    const int N = 8;

    // Specify a stride:
    const int stride = 1;

    // Scale the vector:
    c_sscal( N, 5.0f, x, stride );

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

    // Scale the vector using alternative indexing semantics:
    c_sscal_ndarray( N, 5.0f, x, -stride, N-1 );

    // 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">

* * *

## See Also

-   <span class="package-name">[`@stdlib/blas/base/daxpy`][@stdlib/blas/base/daxpy]</span><span class="delimiter">: </span><span class="description">multiply a vector `x` by a constant and add the result to `y`.</span>
-   <span class="package-name">[`@stdlib/blas/base/dscal`][@stdlib/blas/base/dscal]</span><span class="delimiter">: </span><span class="description">multiply a double-precision floating-point vector by a constant.</span>
-   <span class="package-name">[`@stdlib/blas/base/gscal`][@stdlib/blas/base/gscal]</span><span class="delimiter">: </span><span class="description">multiply a vector by a scalar constant.</span>
-   <span class="package-name">[`@stdlib/blas/base/saxpy`][@stdlib/blas/base/saxpy]</span><span class="delimiter">: </span><span class="description">multiply a vector `x` by a constant and add the result to `y`.</span>

</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">

[blas]: http://www.netlib.org/blas

[sscal]: 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

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

[@stdlib/blas/base/daxpy]: https://github.com/stdlib-js/blas/tree/main/base/daxpy

[@stdlib/blas/base/dscal]: https://github.com/stdlib-js/blas/tree/main/base/dscal

[@stdlib/blas/base/gscal]: https://github.com/stdlib-js/blas/tree/main/base/gscal

[@stdlib/blas/base/saxpy]: https://github.com/stdlib-js/blas/tree/main/base/saxpy

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

</section>

<!-- /.links -->
