On 23/09/2008, at 14:59, Roman Leshchinskiy wrote:
dotp :: [:Int:] -> [:Int:] -> Int
dotp v w = I.sumP [: (I.*) x y | x <- v, y <- w :]
The way the vectoriser works at the moment, it will repeat the array
w (lengthP v) times, i.e., create an array of length (lengthP v *
lengthP w). This is quite unfortunate and needs to be fused away but
isn't at the moment. The only advice I can give is to stay away from
array comprehensions for now. They work but are extremely slow. This
definition should work fine:
dotp v w = I.sumP (zipWithP (I.*) v w)
Actually, I didn't pay attention when I wrote this. The two are not
equivalent, of course. Only the second one computes the dot product.
With comprehensions, you'd have to write
dotp v w = [: (I.*) x y | x <- v | y <- w :]
I suspect that will perform reasonably even now.
Roman
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