module StdArrays where

--import Data.Array.Unboxed
import Data.Array


matMult         :: Array (Int,Int) Double -> Array (Int,Int) Double -> Array (Int,Int) Double
matMult x y     =  array resultBounds
                         [((i,j), sum [x!(i,k) * y!(k,j) | k <- range (lj,uj)])
                                       | i <- range (li,ui),
                                         j <- range (lj',uj') ]
        where ((li,lj),(ui,uj))         =  bounds x
              ((li',lj'),(ui',uj'))     =  bounds y
              resultBounds
                | (lj,uj)==(li',ui')    =  ((li,lj'),(ui,uj'))
                | otherwise             = error "matMult: incompatible bounds"


matMult' x y     =  accumArray (+) 0 resultBounds
                              [((i,j), x!(i,k) * y!(k,j))
                                      | i <- range (li,ui),
                                        j <- range (lj',uj'),
                                        k <- range (lj,uj)  ]
        where ((li,lj),(ui,uj))         =  bounds x
              ((li',lj'),(ui',uj'))     =  bounds y
              resultBounds
                | (lj,uj)==(li',ui')    =  ((li,lj'),(ui,uj'))
                | otherwise             = error "matMult: incompatible bounds"