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# gaxpb

> Multiply each element in a strided array by a scalar constant and add a scalar constant to each result.

<section class="usage">

## Usage

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

#### gaxpb( N, alpha, beta, x, strideX )

Multiplies each element in a strided array `x` by a scalar constant `alpha` and adds a scalar constant `beta` to each result.

```javascript
var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];

gaxpb( x.length, 5.0, 3.0, x, 1 );
// x => [ -7.0, 8.0, 18.0, -22.0, 23.0, 3.0, -2.0, -12.0 ]
```

The function has the following parameters:

-   **N**: number of indexed elements.
-   **alpha**: first scalar constant.
-   **beta**: second scalar constant.
-   **x**: input [`Array`][mdn-array] or [`typed array`][mdn-typed-array].
-   **strideX**: stride length.

The `N` and stride parameters determine which elements in the strided array are accessed at runtime. For example, to multiply every other element by `alpha` and add `beta`:

```javascript
var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];

gaxpb( 4, 5.0, 3.0, x, 2 );
// x => [ -7.0, 1.0, 18.0, -5.0, 23.0, 0.0, -2.0, -3.0 ]
```

Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][mdn-typed-array] views.

```javascript
var Float64Array = require( '@stdlib/array/float64' );

// Initial array...
var x0 = new Float64Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );

// Create an offset view...
var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element

// Multiply every other element by 5.0 and add 3.0...
gaxpb( 3, 5.0, 3.0, x1, 2 );
// x0 => <Float64Array>[ 1.0, -7.0, 3.0, -17.0, 5.0, -27.0 ]
```

#### gaxpb.ndarray( N, alpha, beta, x, strideX, offsetX )

Multiplies each element in a strided array `x` by a scalar constant `alpha` and adds a scalar constant `beta` to each result using alternative indexing semantics.

```javascript
var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];

gaxpb.ndarray( x.length, 5.0, 3.0, x, 1, 0 );
// x => [ -7.0, 8.0, 18.0, -22.0, 23.0, 3.0, -2.0, -12.0 ]
```

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:

```javascript
var x = [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ];

gaxpb.ndarray( 3, 5.0, 3.0, x, 1, x.length-3 );
// x => [ 1.0, -2.0, 3.0, -17.0, 28.0, -27.0 ]
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

-   If `N <= 0`, both functions return `x` unchanged.
-   Both functions support array-like objects having getter and setter accessors for array element access (e.g., [`@stdlib/array/base/accessor`][@stdlib/array/base/accessor]).

</section>

<!-- /.notes -->

<section class="examples">

## Examples

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

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

var x = discreteUniform( 10, -100, 100, {
    'dtype': 'float64'
});
console.log( x );

gaxpb( x.length, 5.0, 3.0, x, 1 );
console.log( x );
```

</section>

<!-- /.examples -->

<!-- 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">

[mdn-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array

[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray

[@stdlib/array/base/accessor]: https://www.npmjs.com/package/@stdlib/array-base-accessor

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

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</section>

<!-- /.links -->
