# [R] Fibonacci

David Winsemius dwinsemius at comcast.net
Thu Apr 21 17:44:19 CEST 2011

```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
>  1.618034
> > fib <- function(n) {(phi ^ n - (1 - phi) ^ n) / sqrt(5)}
> > fib(1:10)
>   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)
  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)
 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
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help