Fibonacci

-----Original Message-----
From: r-help-bounces at r-project.org 
[mailto:r-help-bounces at r-project.org] On Behalf Of Nordlund, 
Dan (DSHS/RDA)
Sent: Thursday, April 21, 2011 9:19 AM
To: r-help at r-project.org
Subject: Re: [R] Fibonacci

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
project.org] On Behalf Of David Winsemius
Sent: Thursday, April 21, 2011 8:44 AM
To: Michael Dewey
Cc: r-help at r-project.org
Subject: Re: [R] Fibonacci


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

I, too, like the Michael/David/Wikipedia solution.  But if 
this is homework, I would recommend using length() instead of 
max() for getting the last two items of the vector.

Hope this is helpful,

Dan

Daniel J. Nordlund
Washington State Department of Social and Health Services
Planning, Performance, and Accountability
Research and Data Analysis Division
Olympia, WA 98504-5204