npm package: @stdlib/math-iter-sequences-negalucas
Description: Create an iterator which generates a negaLucas sequence.
Author: The Stdlib Authors
Latest version: 0.2.3

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# iterNegaLucasSeq

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> Create an iterator which generates a [negaLucas sequence][lucas-number].

<!-- 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">

The [negaLucas numbers][lucas-number] are the integer sequence

<!-- <equation class="equation" label="eq:negalucas_sequence" align="center" raw="2, -1, 3, -4, 7, -11, 18, -29, 47, -76, 123, -199, 322, \ldots" alt="NegaLucas sequence"> -->

<div class="equation" align="center" data-raw-text="2, -1, 3, -4, 7, -11, 18, -29, 47, -76, 123, -199, 322, \ldots" data-equation="eq:negalucas_sequence">
    <img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@aa77a2f6e76d2e9da5b49bffa45ee5167d6c16e1/lib/node_modules/@stdlib/math/iter/sequences/negalucas/docs/img/equation_negalucas_sequence.svg" alt="NegaLucas sequence">
    <br>
</div> -->

<!-- </equation> -->

The sequence is defined by the recurrence relation

<!-- <equation class="equation" label="eq:negalucas_recurrence_relation" align="center" raw="L_{n-2} = L_{n} - L_{n-1}" alt="NegaLucas sequence recurrence relation"> -->

<!-- <div class="equation" align="center" data-raw-text="L_{n-2} = L_{n} - L_{n-1}" data-equation="eq:negalucas_recurrence_relation">
    <img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@aa77a2f6e76d2e9da5b49bffa45ee5167d6c16e1/lib/node_modules/@stdlib/math/iter/sequences/negalucas/docs/img/equation_negalucas_recurrence_relation.svg" alt="NegaLucas sequence recurrence relation">
    <br>
</div> -->

<!-- </equation> -->

which yields

<!-- <equation class="equation" label="eq:negalucas_lucas" align="center" raw="L_{-n} = (-1)^{n} L_n" alt="NegaLucas relationship to Lucas numbers"> -->

<!-- <div class="equation" align="center" data-raw-text="L_{-n} = (-1)^{n} L_n" data-equation="eq:negalucas_lucas">
    <img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@aa77a2f6e76d2e9da5b49bffa45ee5167d6c16e1/lib/node_modules/@stdlib/math/iter/sequences/negalucas/docs/img/equation_negalucas_lucas.svg" alt="NegaLucas relationship to Lucas numbers">
    <br>
</div>

<!-- </equation> -->

with seed values `L_0 = 2` and `L_{-1} = -1`.

</section>

<!-- /.intro -->

<!-- Package usage documentation. -->

<section class="installation">

## Installation

```bash
npm install @stdlib/math-iter-sequences-negalucas
```

</section>

<section class="usage">

## Usage

```javascript
var iterNegaLucasSeq = require( '@stdlib/math-iter-sequences-negalucas' );
```

#### iterNegaLucasSeq( \[options] )

Returns an iterator which generates a [negaLucas sequence][lucas-number].

```javascript
var it = iterNegaLucasSeq();
// returns <Object>

var v = it.next().value;
// returns 2

v = it.next().value;
// returns -1

v = it.next().value;
// returns 3

// ...
```

The returned iterator protocol-compliant object has the following properties:

-   **next**: function which returns an iterator protocol-compliant object containing the next iterated value (if one exists) assigned to a `value` property and a `done` property having a `boolean` value indicating whether the iterator is finished.
-   **return**: function which closes an iterator and returns a single (optional) argument in an iterator protocol-compliant object.

The function supports the following `options`:

-   **iter**: number of iterations. Default: `77`.

The returned iterator can only generate the first `77` [negaLucas numbers][lucas-number], as larger [negaLucas numbers][lucas-number] cannot be safely represented in [double-precision floating-point format][ieee754]. By default, the function returns an iterator which generates all `77` numbers. To limit the number of iterations, set the `iter` option.

```javascript
var opts = {
    'iter': 2
};
var it = iterNegaLucasSeq( opts );
// returns <Object>

var v = it.next().value;
// returns 2

v = it.next().value;
// returns -1

var bool = it.next().done;
// returns true
```

</section>

<!-- /.usage -->

<!-- Package usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="notes">

## Notes

-   If an environment supports `Symbol.iterator`, the returned iterator is iterable.

</section>

<!-- /.notes -->

<!-- Package usage examples. -->

<section class="examples">

## Examples

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

```javascript
var iterNegaLucasSeq = require( '@stdlib/math-iter-sequences-negalucas' );

// Create an iterator:
var it = iterNegaLucasSeq();

// Perform manual iteration...
var v;
while ( true ) {
    v = it.next();
    if ( v.done ) {
        break;
    }
    console.log( v.value );
}
```

</section>

<!-- /.examples -->

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<section class="references">

</section>

<!-- /.references -->

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<section class="related">

* * *

## See Also

-   <span class="package-name">[`@stdlib/math-base/special/negalucas`][@stdlib/math/base/special/negalucas]</span><span class="delimiter">: </span><span class="description">compute the nth negaLucas number.</span>
-   <span class="package-name">[`@stdlib/math-iter/sequences/lucas`][@stdlib/math/iter/sequences/lucas]</span><span class="delimiter">: </span><span class="description">create an iterator which generates a Lucas sequence.</span>
-   <span class="package-name">[`@stdlib/math-iter/sequences/negafibonacci`][@stdlib/math/iter/sequences/negafibonacci]</span><span class="delimiter">: </span><span class="description">create an iterator which generates a negaFibonacci sequence.</span>

</section>

<!-- /.related -->

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* * *

## 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].

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## License

See [LICENSE][stdlib-license].


## Copyright

Copyright &copy; 2016-2026. The Stdlib [Authors][stdlib-authors].

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[lucas-number]: https://en.wikipedia.org/wiki/Lucas_number

[ieee754]: https://en.wikipedia.org/wiki/IEEE_754-1985

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