[Haskell-cafe] Haskell, C and Matrix Multiplication

[Blake Rain]

On Mon, 2011-01-17 at 10:13 +0000, Pedro Vasconcelos wrote: 
> On Mon, 17 Jan 2011 07:45:04 +0000
> Blake Rain <blake.rain at gmail.com> 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
> 
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