time-to-botec/squiggle/node_modules/@stdlib/math/iter/sequences/negafibonacci/README.md

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# iterNegaFibonacciSeq

> Create an iterator which generates a [negaFibonacci sequence][fibonacci-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 [negaFibonacci numbers][fibonacci-number] are the integer sequence

<!-- <equation class="equation" label="eq:negafibonacci_sequence" align="center" raw="0, 1, -1, 2, -3, 5, -8, 13, -21, 34, -55, 89, -144, \ldots" alt="NegaFibonacci sequence"> -->

<div class="equation" align="center" data-raw-text="0, 1, -1, 2, -3, 5, -8, 13, -21, 34, -55, 89, -144, \ldots" data-equation="eq:negafibonacci_sequence">
    <img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@aa77a2f6e76d2e9da5b49bffa45ee5167d6c16e1/lib/node_modules/@stdlib/math/iter/sequences/negafibonacci/docs/img/equation_negafibonacci_sequence.svg" alt="NegaFibonacci sequence">
    <br>
</div>

<!-- </equation> -->

The sequence is defined by the recurrence relation

<!-- <equation class="equation" label="eq:negafibonacci_recurrence_relation" align="center" raw="F_{n-2} = F_{n} - F_{n-1}" alt="NegaFibonacci sequence recurrence relation"> -->

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

<!-- </equation> -->

which yields

<!-- <equation class="equation" label="eq:negafibonacci_fibonacci" align="center" raw="F_{-n} = (-1)^{n+1} F_n" alt="NegaFibonacci relationship to Fibonacci numbers"> -->

<div class="equation" align="center" data-raw-text="F_{-n} = (-1)^{n+1} F_n" data-equation="eq:negafibonacci_fibonacci">
    <img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@aa77a2f6e76d2e9da5b49bffa45ee5167d6c16e1/lib/node_modules/@stdlib/math/iter/sequences/negafibonacci/docs/img/equation_negafibonacci_fibonacci.svg" alt="NegaFibonacci relationship to Fibonacci numbers">
    <br>
</div>

<!-- </equation> -->

with seed values `F_0 = 0` and `F_{-1} = 1`.

</section>

<!-- /.intro -->

<!-- Package usage documentation. -->

<section class="usage">

## Usage

```javascript
var iterNegaFibonacciSeq = require( '@stdlib/math/iter/sequences/negafibonacci' );
```

#### iterNegaFibonacciSeq( \[options] )

Returns an iterator which generates a [negaFibonacci sequence][fibonacci-number].

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

var v = it.next().value;
// returns 0

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

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

// ...
```

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: `79`.

The returned iterator can only generate the first `79` [negaFibonacci numbers][fibonacci-number], as larger [Fibonacci numbers][fibonacci-number] cannot be safely represented in [double-precision floating-point format][ieee754]. By default, the function returns an iterator which generates all `79` numbers. To limit the number of iterations, set the `iter` option.

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

var v = it.next().value;
// returns 0

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 iterNegaFibonacciSeq = require( '@stdlib/math/iter/sequences/negafibonacci' );

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

// 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>

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<section class="links">

[fibonacci-number]: https://en.wikipedia.org/wiki/Fibonacci_number

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

</section>

<!-- /.links -->