Hi,
there is a ticket for 'vector' available with what I need:
http://trac.haskell.org/vector/ticket/15
basically, I need a generalised scan that makes available a partially
initialized vector for each new element.
gen_scan :: Vector v a => Int -> (v a -> a) -> v a
Only that 'a' tends to be a 5-tuple ;-)
A function along those lines is extremely useful in a number of cases. I
hope to have some time to actually dig through the repa sources and see
what is possible.
Gruss,
Christian
* Ben Lippmeier
On 19/05/2011, at 8:27 PM, Christian Höner zu Siederdissen wrote:
I'd like to use repa in a rather perverted mode, I guess:
for my programs I need to be able to update arrays in place and repeatedly perform operations on them. Right now, it basically works like this (in ST):
- create unboxed space using "primitive" (same as unboxed vectors) - unsafefreeze unboxed space - perform calculations on frozen, immutable space - write result into mutable space (which is shared with the unsafefrozen space)
If you care deeply about inplace update, then you could use the parallel array filling functions directly. The ones in D.A.Repa.Internals.Eval*.hs. For 2D images, use the fillVectorBlockwiseP [1] or fillCursoredBlock2P.
fillVectorBlockwiseP :: Elt a => IOVector a -- ^ vector to write elements into -> (Int -> a) -- ^ fn to evaluate an element at the given index -> Int -- ^ width of image. -> IO ()
-- | Fill a block in a 2D image, in parallel. -- Coordinates given are of the filled edges of the block. -- We divide the block into columns, and give one column to each thread. fillCursoredBlock2P :: Elt a => IOVector a -- ^ vector to write elements into -> (DIM2 -> cursor) -- ^ make a cursor to a particular element -> (DIM2 -> cursor -> cursor) -- ^ shift the cursor by an offset -> (cursor -> a) -- ^ fn to evaluate an element at the given index. -> Int -- ^ width of whole image -> Int -- ^ x0 lower left corner of block to fill -> Int -- ^ y0 (low x and y value) -> Int -- ^ x1 upper right corner of block to fill -> Int -- ^ y1 (high x and y value, index of last elem to fill) -> IO ()
Actually, it might be worthwhile exporting these in the API anyway.
[1] http://code.ouroborus.net/repa/repa-head/repa/Data/Array/Repa/Internals/Eval... [2] http://code.ouroborus.net/repa/repa-head/repa/Data/Array/Repa/Internals/Eval...
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Christian Höner zu Siederdissen