Re: [Haskell-cafe] Haskell, C and Matrix Multiplication

On Mon, 2011-01-17 at 10:13 +0000, Pedro Vasconcelos wrote:

On Mon, 17 Jan 2011 07:45:04 +0000 Blake Rain wrote:

...

So, after drinking some coffee and having a smoke, I started the Haskell version:

[foldl (+) 0 $ zipWith (*) x y | x <- m1, y <- transpose m2]

I don't think this is correct; it's type is

(Num a) => [[a]] -> [[a]] -> [a]

rather than the expected

(Num a) => [[a]] -> [[a]] -> [[a]]

How about:

mult m1 m2 = [[foldl (+) 0 $ zipWith (*) x y | y<-transpose m2] | x<-m1]

So sorry, I meant: mult :: (Num a) => [[a]] -> [[a]] -> [a] mult m1 m2 = [foldl (+) 0 $ zipWith (*) x y | x <- m1, y <- transpose m2] Lack of sleep.

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.

Regards,

Pedro

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe