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. When I try any kind of index manipulations, the compiler invariably tells me that it does not want to build [: :] - lists of indices (e.g., there is no enumFromToP) (I guess because I'm using Data.Array.Parallel.Prelude.Double) Puzzled - J.W. PS: what's the recommended way to multiply matrices (better modelled as Array (Int,Int) Double or [[Double]] ?) with the par/pseq approach (if this is recommended at all)? As I said earlier, I just want to have some nice and easy benchmarks for demonstration in a lecture (to be run on 2, 4, or 8 cores). Of course if they work, I'd use them in real life as well... _______________________________________________ Haskell-Cafe mailing list [hidden email] http://www.haskell.org/mailman/listinfo/haskell-cafe signature.asc (268 bytes) Download Attachment |
I never used DPH, but for Matrices, I always tend to use Array (Int,Int) Double, as it accesses its elements in O(1). Arrays also can be unboxed (UArray), which are much faster, or monadic and mutable (MArray), which are more flexible.
I don't know if it is possible to use Arrays with DPH... On Sun, Jan 17, 2010 at 21:35, Johannes Waldmann <[hidden email]> wrote: Hello. -- Rafael Gustavo da Cunha Pereira Pinto _______________________________________________ Haskell-Cafe mailing list [hidden email] http://www.haskell.org/mailman/listinfo/haskell-cafe |
In reply to this post by Johannes Waldmann
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 _______________________________________________ Haskell-Cafe mailing list [hidden email] http://www.haskell.org/mailman/listinfo/haskell-cafe |
In reply to this post by Rafael Gustavo da Cunha Pereira Pinto-2
> ... use Array (Int,Int) Double, as it accesses its elements in O(1). thanks for the comments. I don't need O(dim^0) element access - I need O(dim^reasonable) addition and multiplication. Modelling a matrix as [[Element]] should be nearly fine (for sequential execution), I think these are quadratic/cubic: a * b = zipWith (zipWith (+)) a b a * b = for a $ \ row -> for ( transpose b ) $ \ col -> sum $ zipWith (*) row col The only problem with this code is that 'transpose b' (assuming the compiler lifts it to outer scope) allocates memory that later becomes garbage, but not immediately, since it is needed several times. ( in the above, for = flip map , which is missing from the standard libs? by analogy to forM = flip mapM ) Best regards, J.W. _______________________________________________ Haskell-Cafe mailing list [hidden email] http://www.haskell.org/mailman/listinfo/haskell-cafe |
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