On Friday 27 September 2002 05:19 pm, Hal Daume III wrote:
> There is a one pass solution using mfix. This looks like:
>
> mfix (\ ~s -> ioaA a 1 s)
>
> where ioaA is defined as:
>
> ioaA a i s
>
> | i > sz = return 0
> | otherwise =
>
> do s' <- ioaA a (i+1) s
> v <- readArray a i
> writeArray a i (v/s)
> return (s' + v)
> where (_,sz) = Data.Array.IO.bounds a
>
> Using unboxed arrays is not possible in the fixed point version
> (loop). On the normal version, it just about triples the speed across the
> board.
Hi,
I'm not sure if it's mfix we should blame here. Can you please
experiment with the following version of normalize and report on
running times?
norm a = mdo s <- ioaA 1 s id
return ()
where (_, sz) = bounds a
ioaA i s acc
| i > sz = return (acc 0)
| True =
do v <- readArray a i
writeArray a i (v/s)
ioaA (i+1) s (\x -> v + acc x)
It'd be interesting to see the results especially for very large
inputs (i.e. >= half a million elements.)
-Levent.
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