On Sun, Nov 15, 2009 at 5:50 PM, Felipe Lessa
On Sun, Nov 15, 2009 at 03:00:34PM +0300, Alexey Khudyakov wrote:
Naive implementation using lists and index lookup. 2.15 second for 200*200 array
sliceXlist :: Int -> UArr Double -> [UArr Double] sliceXlist n a = map mkSlice [0 .. n-1] where mkSlice x = toU $ map (\y -> indexU a (x + y*n)) [0 .. n-1]
Have you tried something like
mkSlice x = mapU (\y -> indexU a (x + y*n)) $ enumFromToU 0 (n-1)
I guess it should be a lot faster :).
No it doesn't. There is no significant difference between two variant above. I think any program which uses indexU will be slowed to crawl. Seems like a bug for me.
Another implementation you may try is
a' = mapU (\(i :*: x) -> (i `mod` n) :*: x) (indexedU a) mkSlice j = fstU $ filterU (\(i :*: x) -> i == j) a'
This one is fastest so far
Also, I would recomend using criterion.
I tried to do so.. But it depends on gtk2hs and it is too difficult to install