many parallel applications of a sequential transform in repa

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Here’s a possible modified version of your code, using delayed arrays:

  {-# LANGUAGE TypeOperators #-}

  import Data.Array.Repa as R

  mulM :: (Num a, Source r a) => Array r DIM2 a -> Array D DIM2 a
  mulM arr = traverse arr id mulM'
  where
  mulM' _ idx@(i' :. i) =
  sumAllS $ extract (Z:.0) (Z:.(i+1)) $ slice arr (i' :. All)

  ext :: DIM2
  ext = Z :. (1000000::Int) :. (10::Int)

  array :: Array D DIM2 Int
  array = fromFunction ext (\(Z:.j:.i) -> j+i)

  main :: IO ()
  main = do
  let delayedArray :: Array D DIM2 Int
  delayedArray = delay array
  result = computeUnboxedS $ mulM delayedArray
  print "done"

Please note that this is a simplified example, and you may need to adapt and experiment further with Repa’s features to fully capture the desired linear-work algorithm for your specific matrix M. Be sure to refer to Repa’s documentation for more information on its capabilities and how to best express your computations.

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