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R031E5
December 23rd, 2008, 09:18 PM
Hi! I'm having a really hard time figuring out if there's some programming language in which I can write the fibonacci sequence with only two variables.

The normal syntax is (as everybody knows):

z = x + y
x = y
y = z

But I'm just curious
I hope someone can help me with that

Cheers!

Gilabuugs
December 23rd, 2008, 09:29 PM
something like?
http://code.activestate.com/recipes/66316/

monkeyking
December 23rd, 2008, 10:15 PM
or just do it analytically with one variabel

http://upload.wikimedia.org/math/e/a/2/ea28b263d7f01d652ebc064d0ee0e26b.png

PandaGoat
December 24th, 2008, 05:15 AM
I do not think you can do what you are asking since that is not how a sequence is even defined. If you want the nth number you must build up to it using recursion or iteration. There is no language that implements any of these methods with simple assignments. Although, this sequence is closely tied to the golden ratio, and the nth number can be approximated, as the above poster pointed out.

The closest thing I can think of for a language where you can do what you want is Haskell where variables are not evaluated until they are needed, although I am sure there are other language.

monkeyking
December 24th, 2008, 05:56 AM
... If you want the nth numbers youmust build up to it using recursion or iteration...

... and the nth number can be approximated, as the above poster pointed out.


Without making a mathdiscussion out of it.
I don't think you are right.

You don't have to build up anything.
If you want to calculate the sum of all values from 0 to n.
You don't actually have to add every single one.
you can simply calculate it by n(n+1)/2.

The formula is not an approximation, it's equally valid.
It broadens the domain for the fib function from the positive integers to the reals. Just as the gamma function has the real axis as domain but contains the factorial function as an injection on the natural numbers.

enjoy the christmas.

slavik
December 24th, 2008, 06:27 AM
using recursion, you need only 2 variables ...

x=1, y=1
odd iterations ...
x+=y;
print x
even iterations ...
y+=x;
print y