Math Related : Improved Fibonacci Sequence

Ben Clarke Feb 4, 2008

General

This script displays a Fibonacci sequence up to a certain number of calculations. It uses a lookup array to offset the large, recursive calculations needed to calculate large numbers, and is not too processor intensive. It is precise to 32 bits (78 iterations), after which the JavaScript interpreter rolls bits over.

Computations:

Notes

Created by: Ben Clarke
Web Site: http://benclarke.ca/

Source Code

Paste this source code into the designated areas.

External file

Paste this code into an external JavaScript file named: impFibonacciSeq.js

/* This script and many more are available free online at
The JavaScript Source!! http://www.javascriptsource.com
Created by: Ben Clarke | http://benclarke.ca/ */

var i=0;
var fibs = []; // lookup table so it doesn't take forever
		
function fib(a) {
	var x, y, z;
	switch(a) {
		case 0: case 1: x = a; break;
		default:
			if(!fibs[a - 1]) {
				fibs[a - 1] = fib(a - 1);
			}
			if(!fibs[a - 2]) {
				fibs[a - 2] = fib(a - 2);
			}
			
			y = fibs[a - 1];
			z = fibs[a - 2];
			x = y + z;
	}
	return x;
}

function doFib() {
	
	var n = parseInt(document.getElementById("n").value);
	if(isNaN(n) || n < 1) { 
		alert("Please enter a positive number for computations");
		return;
	}
	
	var a;
	var r = document.getElementById("r");
	r.value = "";
	
	for(var i=0; i<n; i++) {
		a = fib(i);
		r.value += " " + a;
	}
}

Head

Paste this code into the HEAD section of your HTML document.


<script type="text/javascript" src="impFibonacciSeq.js"></script>

Body

Paste this code into the BODY section of your HTML document


<p>
Computations: <input type="text" id="n"/></p>
<p>
<input type="text" id="r" style="width: 500px;"/></p>
<p>
<input type="button" onclick="doFib();" value="Calculate"/></p>

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