Johannes Waldmann wrote:
Hello.
How can I multiply matrices (of Doubles) with dph (-0.4.0)? (ghc-6.12.1) - I was trying
type Vector = [:Double:] type Matrix = [:Vector:]
times :: Matrix -> Matrix -> Matrix times a b = mapP ( \ row -> mapP ( \ col -> sumP ( zipWithP (*) row col ) ) ( transposeP b ) ) a
but there is no such thing as transposeP.
It's possible to implement transposeP as follows, {-# LANGUAGE PArr #-} ... import qualified Data.Array.Parallel.Prelude.Int as I transposeP :: Matrix -> Matrix transposeP a = let h = lengthP a w = lengthP (a !: 0) rh = I.enumFromToP 0 (h I.- 1) -- or [: 0 .. h I.- 1 :] rw = I.enumFromToP 0 (w I.- 1) -- or [: 0 .. w I.- 1 :] in if h == 0 then [: :] else mapP (\y -> mapP (\x -> a !: x !: y) rh) rw Maybe there is a better way? Bertram