On Mon, 17 Jan 2011 10:38:30 +0000
Blake Rain
So sorry, I meant:
mult :: (Num a) => [[a]] -> [[a]] -> [a] mult m1 m2 = [foldl (+) 0 $ zipWith (*) x y | x <- m1, y <- transpose m2]
Shouldn't the result of multiplying an (n,k)-matrix by an (k,m)-matrix be an (n,m)-matrix? The way you've written it the result will be a list of length n*m.
Regarding performance: did you make sure you're forcing the evaluation of the result matrix?
I thought I was. It's printing the results as expected. Could be I'm just imagining I am and suffering a delusion or misunderstanding.
Another issue to look out for is let-floating: if you perform the same matrix multiplication repeatedly, the compiler might very well lift the matrix calculation outside the loop. Pedro