From: jzakiya <jzakiya@...>
Date: 2009-07-13T02:15:06+09:00
Subject: Re: Fibonacci numbers - newbie question.

On Jul 12, 5:40 am, Stefano Crocco <stefano.cro...@alice.it> wrote:
> On Sunday 12 July 2009, salai wrote:
>
>
>
> > |Dear All,
> > |
> > |I have two Fibonacci method, and I got different result.
> > |
> > |What wrong in my code.?
> > |
> > |def fib(n)
> > |  if n < 2
> > |          1
> > |  else
> > |          fib(n-2) + fib(n-1)
> > |  end
> > |end
> > |
> > |puts fib(10) # ---> 89
> > |
> > |
> > |def fib1(x)
> > |  return x if x < 2
> > |  return fib1(x- 1) + fib1(x - 2)
> > |end
> > |
> > |
> > |
> > |puts fib1(10) # --> 55
> > |
> > |
> > |regards,
> > |salai.
>
> In the first case, if the number is less than 2, you always return 1. In the
> second case, you return the number itself (that is, 1 if x is 1 and 0 if x is
> 0).
>
> Stefano

Many people forget (or don't know) the series starts:

Fib(0)=0
Fib(1)=1
Fib(2)=1
....
So when x < 2 then Fib=x
These initial conditions are important for doing algebraic forms for
the series.

And actually, the full series can be extended into negative numbers.
See at url: http://en.wikipedia.org/wiki/Fibonacci_number