R help - Apr 2011 - Fibonacci

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.

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]]

The "easy" solution to compute the Fibonacci numbers is
 
fibo <- function(n,a=1,b=1){
 if (n == 1) return(a)
 if (n == 2) return(b)
 return(fibo(n-1,b,a+b)) 
}

It avoids double recursion.
It is, however, not as resource efficient as a loop since R does not do
tail recursion elimination.




On Apr 20, 2011, at 11:42 AM, 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.
> 
> 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]]
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

On Wed, Apr 20, 2011 at 11:42:38AM +0200, 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.
> 
> 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)
Is it allowed to use length() function? If so, then try
the following

  Fibonacci<-c(1,1)
  while (max(Fibonacci)<500){
      Fibonacci<-c(Fibonacci, Fibonacci[length(Fibonacci) - 1] +
Fibonacci[length(Fibonacci)])
  }

Petr Savicky.

Fibonacci <- c(1, 1)
while (max (Fibonacci) < 500){
  Fibonacci <- c(Fibonacci, sum(tail(Fibonacci, 2))) } 

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of Georgina Imberger
Sent: Wednesday, April 20, 2011 5:43 AM
To: r-help at r-project.org
Subject: [R] Fibonacci

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.

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]]

______________________________________________
R-help at r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.


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Another solution:

while (Fibonacci[1] < 500)  Fibonacci <- c(sum(Fibonacci[c(1,2)]),
Fibonacci)

While this adds the sum before the existing values, the length or tail
function or avoided, but even with reordering, its faster
(Fibonacci[length(Fibonacci):1])

Best regards

Bart


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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

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