[Haskell-cafe] The maths behind the Fastest Fibb In The West.
erantapaa at gmail.com
Sat May 7 02:38:35 UTC 2016
On Friday, May 6, 2016 at 6:46:26 PM UTC-5, Michael Litchard wrote:
> I've been working on a project that needs a good fibonacci generator, and
> I'm to the point where can now improve upon this one:
> thanks to this guy:
> He suggested breaking up a guard into two diffeent functions, which I can
> do, but I don't know what to call them because I don't know why the
> operations are different. I'm referring to this section:
> fib' (f, g) p
> | p = (f*(f+2*g), f^2 + g^2)
> | otherwise = (f^2+g^2, g*(2*f-g))
> I'd like to know the reason why each guard does two entirely different things, so I know what to call the functions when I seperate them out.
Clearly `p` is a Bool, and it comes from the expression:
map (toEnum . fromIntegral) $ unfoldl divs n
What's going on in `toEnum . fromIntegral` is that a remainder (either 0 or
1 - it blows up for anything else) is being converted to a Bool, with 0
mapping to False and 1 mapping to True. So `isOdd` would be a more
descriptive name for `p`.
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