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https://github.com/stdlib-js/blas-base-gdot

Calculate the dot product of two vectors.
https://github.com/stdlib-js/blas-base-gdot

algebra blas ddot dot dot-product inner javascript level-1 linear math mathematics node node-js nodejs product scalar scalar-product sdot stdlib subroutines

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Calculate the dot product of two vectors.

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README 

        



  

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# gdot



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



> Calculate the dot product of two vectors.



The [dot product][dot-product] (or scalar product) is defined as



```math

\mathbf{x}\cdot\mathbf{y} = \sum_{i=0}^{N-1} x_i y_i = x_0 y_0 + x_1 y_1 + \ldots + x_{N-1} y_{N-1}

```



## Installation



```bash

npm install @stdlib/blas-base-gdot

```



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 gdot = require( '@stdlib/blas-base-gdot' );

```



#### gdot( N, x, strideX, y, strideY )



Calculates the dot product of vectors `x` and `y`.



```javascript

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

var y = [ 2.0, 6.0, -1.0, -4.0, 8.0 ];



var z = gdot( x.length, x, 1, y, 1 );

// returns -5.0

```



The function has the following parameters:



-   **N**: number of indexed elements.

-   **x**: first input [`Array`][mdn-array] or [`typed array`][mdn-typed-array].

-   **strideX**: index increment for `x`.

-   **y**: second input [`Array`][mdn-array] or [`typed array`][mdn-typed-array].

-   **strideY**: index increment for `y`.



The `N` and stride parameters determine which elements in the strided arrays are accessed at runtime. For example, to calculate the dot product of every other value in `x` and the first `N` elements of `y` in reverse order,



```javascript

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

var y = [ 1.0, 1.0, 1.0, 1.0, 1.0, 1.0 ];



var z = gdot( 3, x, 2, y, -1 );

// returns 9.0

```



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 arrays...

var x0 = new Float64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );

var y0 = new Float64Array( [ 7.0, 8.0, 9.0, 10.0, 11.0, 12.0 ] );



// Create offset views...

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

var y1 = new Float64Array( y0.buffer, y0.BYTES_PER_ELEMENT*3 ); // start at 4th element



var z = gdot( 3, x1, -2, y1, 1 );

// returns 128.0

```



#### gdot.ndarray( N, x, strideX, offsetX, y, strideY, offsetY )



Calculates the dot product of `x` and `y` using alternative indexing semantics.



```javascript

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

var y = [ 2.0, 6.0, -1.0, -4.0, 8.0 ];



var z = gdot.ndarray( x.length, x, 1, 0, y, 1, 0 );

// returns -5.0

```



The function has the following additional parameters:



-   **offsetX**: starting index for `x`.

-   **offsetY**: starting index for `y`.



While [`typed array`][mdn-typed-array] views mandate a view offset based on the underlying buffer, the offset parameters support indexing semantics based on starting indices. For example, to calculate the dot product of every other value in `x` starting from the second value with the last 3 elements in `y` in reverse order



```javascript

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

var y = [ 7.0, 8.0, 9.0, 10.0, 11.0, 12.0 ];



var z = gdot.ndarray( 3, x, 2, 1, y, -1, y.length-1 );

// returns 128.0

```



## Notes



-   If `N <= 0` both functions return `0.0`.

-   `gdot()` corresponds to the [BLAS][blas] level 1 function [`ddot`][ddot] with the exception that this implementation works with any array type, not just Float64Arrays. Depending on the environment, the typed versions ([`ddot`][@stdlib/blas/base/ddot], [`sdot`][@stdlib/blas/base/sdot], etc.) are likely to be significantly more performant.



## Examples



```javascript

var discreteUniform = require( '@stdlib/random-array-discrete-uniform' );

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



var opts = {

    'dtype': 'float64'

};

var x = discreteUniform( 10, 0, 500, opts );

console.log( x );



var y = discreteUniform( x.length, 0, 255, opts );

console.log( y );



var out = gdot.ndarray( x.length, x, 1, 0, y, -1, y.length-1 );

console.log( out );

```



* * *



## See Also



-   [`@stdlib/blas-base/ddot`][@stdlib/blas/base/ddot]: calculate the dot product of two double-precision floating-point vectors.

-   [`@stdlib/blas-base/sdot`][@stdlib/blas/base/sdot]: calculate the dot product of two single-precision floating-point vectors.

-   [`@stdlib/blas-gdot`][@stdlib/blas/gdot]: calculate the dot product of two vectors.



* * *



## 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-base-gdot.svg

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



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

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



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

[coverage-url]: https://codecov.io/github/stdlib-js/blas-base-gdot?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-base-gdot/tree/deno

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

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

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

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

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

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



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



[dot-product]: https://en.wikipedia.org/wiki/Dot_product



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



[ddot]: http://www.netlib.org/lapack/explore-html/de/da4/group__double__blas__level1.html



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



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



[@stdlib/blas/gdot]: https://github.com/stdlib-js/blas-gdot