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https://github.com/stdlib-js/math-strided-special-ahavercos-by

Compute the inverse half-value versed cosine of each element retrieved from an input strided array via a callback function.
https://github.com/stdlib-js/math-strided-special-ahavercos-by

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Compute the inverse half-value versed cosine of each element retrieved from an input strided array via a callback function.

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README 

        



  

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# ahavercosBy



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



> Compute the [inverse half-value versed cosine][@stdlib/math/base/special/ahavercos] of each element retrieved from an input strided array via a callback function.



## Installation



```bash

npm install @stdlib/math-strided-special-ahavercos-by

```



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 ahavercosBy = require( '@stdlib/math-strided-special-ahavercos-by' );

```



#### ahavercosBy( N, x, strideX, y, strideY, clbk\[, thisArg] )



Computes the [inverse half-value versed cosine][@stdlib/math/base/special/ahavercos] of each element retrieved from an input strided array `x` via a callback function and assigns each result to an element in an output strided array `y`.



```javascript

function accessor( v ) {

    return v;

}



var x = [ 0.0, 0.5, 1.0, 0.25, 0.75 ];

var y = [ 0.0, 0.0, 0.0, 0.0, 0.0 ];



ahavercosBy( x.length, x, 1, y, 1, accessor );

// y => [ ~3.142, ~1.571, 0.0, ~2.094, ~1.047 ]

```



The function accepts the following arguments:



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

-   **x**: input [`Array`][mdn-array], [`typed array`][mdn-typed-array], or an array-like object (excluding strings and functions).

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

-   **y**: output [`Array`][mdn-array], [`typed array`][mdn-typed-array], or an array-like object (excluding strings and functions).

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

-   **clbk**: callback function.

-   **thisArg**: execution context (_optional_).



The invoked callback function is provided six arguments:



-   **value**: input array element.

-   **idx**: iteration index (zero-based).

-   **xi**: input array strided index (`offsetX + idx*strideX`).

-   **yi**: output array strided index (`offsetY + idx*strideY`).

-   **x**: input array/collection.

-   **y**: output array/collection.



To set the callback execution context, provide a `thisArg`.



```javascript

function accessor( v ) {

    this.count += 1;

    return v;

}



var context = {

    'count': 0

};



var x = [ 0.0, 0.5, 1.0, 0.25, 0.75 ];

var y = [ 0.0, 0.0, 0.0, 0.0, 0.0 ];



ahavercosBy( x.length, x, 1, y, 1, accessor, context );

// y => [ ~3.142, ~1.571, 0.0, ~2.094, ~1.047 ]



var cnt = context.count;

// returns 5

```



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



```javascript

function accessor( v ) {

    return v;

}



var x = [ 0.0, 0.5, 1.0, 0.25, 0.75, 0.68 ];

var y = [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ];



ahavercosBy( 3, x, 2, y, -1, accessor );

// y => [ ~1.047, 0.0, ~3.142, 0.0, 0.0, 0.0 ]

```



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' );



function accessor( v ) {

    return v;

}



// Initial arrays...

var x0 = new Float64Array( [ 0.0, 0.5, 1.0, 0.25, 0.75, 0.68 ] );

var y0 = new Float64Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );



// 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



ahavercosBy( 3, x1, -2, y1, 1, accessor );

// y0 => [ 0.0, 0.0, 0.0, ~1.203, ~2.094, ~1.571 ]

```



#### ahavercosBy.ndarray( N, x, strideX, offsetX, y, strideY, offsetY, clbk\[, thisArg] )



Computes the [inverse half-value versed cosine][@stdlib/math/base/special/ahavercos] of each element retrieved from an input strided array `x` via a callback function and assigns each result to an element in an output strided array `y` using alternative indexing semantics.



```javascript

function accessor( v ) {

    return v;

}



var x = [ 0.0, 0.5, 1.0, 0.25, 0.75 ];

var y = [ 0.0, 0.0, 0.0, 0.0, 0.0 ];



ahavercosBy.ndarray( x.length, x, 1, 0, y, 1, 0, accessor );

// y => [ ~3.142, ~1.571, 0.0, ~2.094, ~1.047 ]

```



The function accepts the following additional arguments:



-   **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 `offsetX` and `offsetY` parameters support indexing semantics based on starting indices. For example, to index every other value in `x` starting from the second value and to index the last `N` elements in `y`,



```javascript

function accessor( v ) {

    return v;

}



var x = [ 0.0, 0.5, 1.0, 0.25, 0.75, 0.68 ];

var y = [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ];



ahavercosBy.ndarray( 3, x, 2, 1, y, -1, y.length-1, accessor );

// y => [ 0.0, 0.0, 0.0, ~1.203, ~2.094, ~1.571 ]

```



## Notes



-   If a provided callback function does not return any value (or equivalently, explicitly returns `undefined`), the value is **ignored**.



    ```javascript

    function accessor() {

        // No-op...

    }



    var x = [ 0.0, 0.5, 1.0, 0.25, 0.75 ];

    var y = [ 0.0, 0.0, 0.0, 0.0, 0.0 ];



    ahavercosBy( x.length, x, 1, y, 1, accessor );

    // y => [ 0.0, 0.0, 0.0, 0.0, 0.0 ]

    ```



## Examples



```javascript

var uniform = require( '@stdlib/random-base-uniform' ).factory;

var filledarray = require( '@stdlib/array-filled' );

var filledarrayBy = require( '@stdlib/array-filled-by' );

var ahavercosBy = require( '@stdlib/math-strided-special-ahavercos-by' );



function accessor( v, i ) {

    if ( (i%3) === 0 ) {

        // Simulate a "missing" value...

        return;

    }

    return v;

}



var x = filledarrayBy( 10, 'generic', uniform( 0.0, 1.0 ) );

console.log( x );



var y = filledarray( null, 10, 'generic' );

console.log( y );



ahavercosBy.ndarray( x.length, x, 1, 0, y, -1, y.length-1, accessor );

console.log( y );

```



* * *



## 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/math-strided-special-ahavercos-by.svg

[npm-url]: https://npmjs.org/package/@stdlib/math-strided-special-ahavercos-by



[test-image]: https://github.com/stdlib-js/math-strided-special-ahavercos-by/actions/workflows/test.yml/badge.svg?branch=main

[test-url]: https://github.com/stdlib-js/math-strided-special-ahavercos-by/actions/workflows/test.yml?query=branch:main



[coverage-image]: https://img.shields.io/codecov/c/github/stdlib-js/math-strided-special-ahavercos-by/main.svg

[coverage-url]: https://codecov.io/github/stdlib-js/math-strided-special-ahavercos-by?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/math-strided-special-ahavercos-by/tree/deno

[deno-readme]: https://github.com/stdlib-js/math-strided-special-ahavercos-by/blob/deno/README.md

[umd-url]: https://github.com/stdlib-js/math-strided-special-ahavercos-by/tree/umd

[umd-readme]: https://github.com/stdlib-js/math-strided-special-ahavercos-by/blob/umd/README.md

[esm-url]: https://github.com/stdlib-js/math-strided-special-ahavercos-by/tree/esm

[esm-readme]: https://github.com/stdlib-js/math-strided-special-ahavercos-by/blob/esm/README.md

[branches-url]: https://github.com/stdlib-js/math-strided-special-ahavercos-by/blob/main/branches.md



[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/math-strided-special-ahavercos-by/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/math/base/special/ahavercos]: https://github.com/stdlib-js/math-base-special-ahavercos