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Groups > comp.lang.python > #5583

Re: Faster Recursive Fibonacci Numbers

From Jussi Piitulainen <jpiitula@ling.helsinki.fi>
Newsgroups comp.lang.python
Subject Re: Faster Recursive Fibonacci Numbers
Date 2011-05-17 20:19 +0300
Organization University of Helsinki
Message-ID <qotmxilp7na.fsf@ruuvi.it.helsinki.fi> (permalink)
References <108ce447-10fa-4cf7-84ef-440ee18dbfd4@22g2000prx.googlegroups.com> <9d9c163b-14fd-4131-81bb-105c3b97c432@h36g2000pro.googlegroups.com> <mailman.1680.1305651743.9059.python-list@python.org>

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geremy condra writes:

> or O(1):
> 
> φ = (1 + sqrt(5)) / 2
> def fib(n):
>     numerator = (φ**n) - (1 - φ)**n
>     denominator = sqrt(5)
>     return round(numerator/denominator)
> 
> Testing indicates that it's faster somewhere around 7 or so.

And increasingly inaccurate from 71 on.

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Thread

Faster Recursive Fibonacci Numbers RJB <rbotting@csusb.edu> - 2011-05-17 08:50 -0700
  Re: Faster Recursive Fibonacci Numbers Ian Kelly <ian.g.kelly@gmail.com> - 2011-05-17 10:23 -0600
  Re: Faster Recursive Fibonacci Numbers rusi <rustompmody@gmail.com> - 2011-05-17 09:25 -0700
  Re: Faster Recursive Fibonacci Numbers rusi <rustompmody@gmail.com> - 2011-05-17 09:36 -0700
    Re: Faster Recursive Fibonacci Numbers geremy condra <debatem1@gmail.com> - 2011-05-17 10:02 -0700
      Re: Faster Recursive Fibonacci Numbers Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2011-05-17 20:19 +0300
        Re: Faster Recursive Fibonacci Numbers geremy condra <debatem1@gmail.com> - 2011-05-17 11:56 -0700
          Re: Faster Recursive Fibonacci Numbers Wolfram Hinderer <wolfram.hinderer@googlemail.com> - 2011-05-17 14:04 -0700
            Re: Faster Recursive Fibonacci Numbers geremy condra <debatem1@gmail.com> - 2011-05-17 14:59 -0700
            Re: Faster Recursive Fibonacci Numbers rusi <rustompmody@gmail.com> - 2011-05-17 21:43 -0700
      Re: Faster Recursive Fibonacci Numbers Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-19 22:47 +0000
        Re: Faster Recursive Fibonacci Numbers Chris Angelico <rosuav@gmail.com> - 2011-05-20 09:37 +1000
          Re: Faster Recursive Fibonacci Numbers Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-20 05:58 +0000
            Re: Faster Recursive Fibonacci Numbers Chris Angelico <rosuav@gmail.com> - 2011-05-20 16:06 +1000
              Re: Faster Recursive Fibonacci Numbers harrismh777 <harrismh777@charter.net> - 2011-05-20 01:26 -0500
                Re: Faster Recursive Fibonacci Numbers Chris Angelico <rosuav@gmail.com> - 2011-05-20 16:54 +1000
                Re: Faster Recursive Fibonacci Numbers Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-20 17:07 +0000
                Re: Faster Recursive Fibonacci Numbers geremy condra <debatem1@gmail.com> - 2011-05-20 11:43 -0700
                Re: Faster Recursive Fibonacci Numbers Chris Angelico <rosuav@gmail.com> - 2011-05-21 10:44 +1000
              Re: Faster Recursive Fibonacci Numbers Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-05-21 20:49 +1200
            Re: Faster Recursive Fibonacci Numbers Ian Kelly <ian.g.kelly@gmail.com> - 2011-05-20 01:26 -0600
            Re: Faster Recursive Fibonacci Numbers Ian Kelly <ian.g.kelly@gmail.com> - 2011-05-20 01:32 -0600
              Re: Faster Recursive Fibonacci Numbers SigmundV <sigmundv@gmail.com> - 2011-05-20 03:53 -0700
        Re: Faster Recursive Fibonacci Numbers geremy condra <debatem1@gmail.com> - 2011-05-19 17:03 -0700
  Re: Faster Recursive Fibonacci Numbers Raymond Hettinger <python@rcn.com> - 2011-05-24 16:44 -0700

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