# iterNegaFibonacciSeq > Create an iterator which generates a [negaFibonacci sequence][fibonacci-number].
The [negaFibonacci numbers][fibonacci-number] are the integer sequence
NegaFibonacci sequence
The sequence is defined by the recurrence relation
NegaFibonacci sequence recurrence relation
which yields
NegaFibonacci relationship to Fibonacci numbers
with seed values `F_0 = 0` and `F_{-1} = 1`.
## 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 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 var v = it.next().value; // returns 0 v = it.next().value; // returns 1 var bool = it.next().done; // returns true ```
## Notes - If an environment supports `Symbol.iterator`, the returned iterator is iterable.
## Examples ```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 ); } ```
[fibonacci-number]: https://en.wikipedia.org/wiki/Fibonacci_number [ieee754]: https://en.wikipedia.org/wiki/IEEE_754-1985