Fwd: [Haskell-cafe] Transpose using array comprehension

[Chris Witte]

I was trying to use the array comprehension of the Data Parallel
Haskell package.

http://haskell.org/haskellwiki/GHC/Data_Parallel_Haskell

for instance I can define

{-# OPTIONS -fparr -fglasgow-exts #-}

module MatTest
where
import GHC.PArr

ident = [:[:1,0:],[:0,1:]:]
aVect = [:4,5:]

dotP :: Num a => [:a:] -> [:a:] -> a
dotP xs ys = sumP [:x * y | x <- xs | y <- ys :]

matVecMul :: Num a => [:[:a:]:] -> [:a:] -> [:a:]
matVecMul xs ys = [:dotP x ys | x <- xs:]


but when I tried to define a matrix matrix multiplication

matMel :: Num a => [:[:a:]:] -> [:[:a:]:] -> [:a:]

I was at a loss for how to do it because i couldn't define transpose.

On 4/18/07, Henning Thielemann <lemming at henning-thielemann.de> wrote:
>
> On Wed, 18 Apr 2007, Chris Witte wrote:
>
> > I just started playing around with GHC.PArr and array comprehension
> > and I was wondering if there is a way to define the transpose of a
> > matrix using array comprehension?
>
> Why not
>
>   let swap :: (i,j) -> (j,i)
>       swap (a,b) = (b,a)
>   in  ixmap (let (lower,upper) = bounds arr in (swap lower, swap upper))
>             swap arr
>
> ?
>