# Re: [R] Fibonacci

From: David Winsemius <dwinsemius_at_comcast.net>
Date: Thu, 21 Apr 2011 11:44:19 -0400

On Apr 21, 2011, at 9:04 AM, Michael Dewey wrote:

> At 10:42 20/04/2011, Georgina Imberger wrote:
>> Hi!
>>
>> I am trying to work out the code to get a Fibonacci sequence, using
>> the
>> while() loop and only one variable. And I can't figure it out.
>
>
> > phi <- 0.5 * (1 + sqrt(5))
> > phi
> [1] 1.618034
> > fib <- function(n) {(phi ^ n - (1 - phi) ^ n) / sqrt(5)}
> > fib(1:10)
> [1] 1 1 2 3 5 8 13 21 34 55
> >
>
> Admittedly this does not use a while loop as you requested

I like it!

> test <-c( 1, 1, 2, 3, 5, 8, 13, 21, 34, 55)  > test == fib(1:10)
[1] TRUE TRUE TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE To avoid such FAQ-tual puzzlement, it might be better to round to zero digits:

fib2 <- function(n) {round( (phi ^ n - (1 - phi) ^ n) / sqrt(5) ) }

> test == fib2(1:10)
[1] TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE There are several packages that offer fib() functions of one name or another, including the gmp package which always seems to "think bigger" than I do. I cannot (trivially) see how that author does it with fibnum(), because it is in a .Call()

```--
David

>
> Courtesy of Wikipedia

>
>
>> Fibonacci<-c(1,1)
>> while (max(Fibonacci)<500){
>> Fibonacci<-c(Fibonacci, (max(Fibonacci) + ?(Fibanacci)))
>> }
>>
>>
>> How can I tell R to take the value one before the max value? (Without
>> defining another variable)
>>
>> (Probably super easy... I am a beginner...)
>>
>> Thanks,
>> Georgie
>>
>>        [[alternative HTML version deleted]]
>
> Michael Dewey
> info_at_aghmed.fsnet.co.uk
> http://www.aghmed.fsnet.co.uk/home.html
>
> ______________________________________________
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> and provide commented, minimal, self-contained, reproducible code.

David Winsemius, MD
West Hartford, CT

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