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https://github.com/stdlib-js/blas-ext-base-gapx

Add a constant to each element in a strided array.
https://github.com/stdlib-js/blas-ext-base-gapx

add addition array blas extended javascript math mathematics ndarray node node-js nodejs scale stdlib strided translate

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Add a constant to each element in a strided array.

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README 

        



  

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# gapx



[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url] 



> Add a constant to each element in a strided array.



## Installation



```bash

npm install @stdlib/blas-ext-base-gapx

```



Alternatively,



-   To load the package in a website via a `script` tag without installation and bundlers, use the [ES Module][es-module] available on the [`esm`][esm-url] branch (see [README][esm-readme]).

-   If you are using Deno, visit the [`deno`][deno-url] branch (see [README][deno-readme] for usage intructions).

-   For use in Observable, or in browser/node environments, use the [Universal Module Definition (UMD)][umd] build available on the [`umd`][umd-url] branch (see [README][umd-readme]).



The [branches.md][branches-url] file summarizes the available branches and displays a diagram illustrating their relationships.



To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.



## Usage



```javascript

var gapx = require( '@stdlib/blas-ext-base-gapx' );

```



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



Adds a constant `alpha` to each element in a strided array `x`.



```javascript

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



gapx( 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 [`Array`][mdn-array] or [`typed array`][mdn-typed-array].

-   **stride**: index increment.



The `N` and `stride` parameters determine which elements in `x` are accessed at runtime. For example, to add a constant to every other element



```javascript

var floor = require( '@stdlib/math-base-special-floor' );



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

var N = floor( x.length / 2 );



gapx( N, 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 Float64Array = require( '@stdlib/array-float64' );

var floor = require( '@stdlib/math-base-special-floor' );



// 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

var N = floor( x0.length/2 );



// Add a constant to every other element...

gapx( N, 5.0, x1, 2 );

// x0 => [ 1.0, 3.0, 3.0, 1.0, 5.0, -1.0 ]

```



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



Adds a constant `alpha` to each element in a strided array `x` using alternative indexing semantics.



```javascript

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



gapx.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 `x`



```javascript

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



gapx.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 `x` unchanged.

-   Depending on the environment, the typed versions ([`dapx`][@stdlib/blas/ext/base/dapx], [`sapx`][@stdlib/blas/ext/base/sapx], etc.) are likely to be significantly more performant.



## Examples



```javascript

var round = require( '@stdlib/math-base-special-round' );

var randu = require( '@stdlib/random-base-randu' );

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

var gapx = require( '@stdlib/blas-ext-base-gapx' );



var rand;

var sign;

var x;

var i;



x = new Float64Array( 10 );

for ( i = 0; i < x.length; i++ ) {

    rand = round( randu()*100.0 );

    sign = randu();

    if ( sign < 0.5 ) {

        sign = -1.0;

    } else {

        sign = 1.0;

    }

    x[ i ] = sign * rand;

}

console.log( x );



gapx( x.length, 5.0, x, 1 );

console.log( x );

```



* * *



## See Also



-   [`@stdlib/blas-ext/base/dapx`][@stdlib/blas/ext/base/dapx]: add a constant to each element in a double-precision floating-point strided array.

-   [`@stdlib/blas-ext/base/sapx`][@stdlib/blas/ext/base/sapx]: add a constant to each element in a single-precision floating-point strided array.



* * *



## Notice



This package is part of [stdlib][stdlib], a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.



For more information on the project, filing bug reports and feature requests, and guidance on how to develop [stdlib][stdlib], see the main project [repository][stdlib].



#### Community



[![Chat][chat-image]][chat-url]



---



## License



See [LICENSE][stdlib-license].



## Copyright



Copyright © 2016-2024. The Stdlib [Authors][stdlib-authors].



[npm-image]: http://img.shields.io/npm/v/@stdlib/blas-ext-base-gapx.svg

[npm-url]: https://npmjs.org/package/@stdlib/blas-ext-base-gapx



[test-image]: https://github.com/stdlib-js/blas-ext-base-gapx/actions/workflows/test.yml/badge.svg?branch=main

[test-url]: https://github.com/stdlib-js/blas-ext-base-gapx/actions/workflows/test.yml?query=branch:main



[coverage-image]: https://img.shields.io/codecov/c/github/stdlib-js/blas-ext-base-gapx/main.svg

[coverage-url]: https://codecov.io/github/stdlib-js/blas-ext-base-gapx?branch=main



[chat-image]: https://img.shields.io/gitter/room/stdlib-js/stdlib.svg

[chat-url]: https://app.gitter.im/#/room/#stdlib-js_stdlib:gitter.im



[stdlib]: https://github.com/stdlib-js/stdlib



[stdlib-authors]: https://github.com/stdlib-js/stdlib/graphs/contributors



[umd]: https://github.com/umdjs/umd

[es-module]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules



[deno-url]: https://github.com/stdlib-js/blas-ext-base-gapx/tree/deno

[deno-readme]: https://github.com/stdlib-js/blas-ext-base-gapx/blob/deno/README.md

[umd-url]: https://github.com/stdlib-js/blas-ext-base-gapx/tree/umd

[umd-readme]: https://github.com/stdlib-js/blas-ext-base-gapx/blob/umd/README.md

[esm-url]: https://github.com/stdlib-js/blas-ext-base-gapx/tree/esm

[esm-readme]: https://github.com/stdlib-js/blas-ext-base-gapx/blob/esm/README.md

[branches-url]: https://github.com/stdlib-js/blas-ext-base-gapx/blob/main/branches.md



[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/blas-ext-base-gapx/main/LICENSE



[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/blas/ext/base/dapx]: https://github.com/stdlib-js/blas-ext-base-dapx



[@stdlib/blas/ext/base/sapx]: https://github.com/stdlib-js/blas-ext-base-sapx