[swannodette]

I'd be curious to know if/how the Clojure code could be written to do this kind of number crunching on GPU. Penumbra has a very idiomatic library for offloading work to the GPU.

[prospero]

I don't have time for a full conversion just now, but an eight-way diffusion on the GPU in Penumbra looks like this:

  (let [sum 0.0
        count 0.0]
    (convolution 1
      (+= sum %1)
      (+= count 1))
    (/ sum count))

"convolution" is a keyword that iterates over the neighbors (with a radius of 1, in this case), and does not overrun the boundaries of the source textures, hence the need to keep a running count.

For a more extensive example, see this implementation of Sobel edge detection on the GPU: http://github.com/ztellman/penumbra/blob/master/src/example/...

[eric_t]

In the Fortran code, this could be run on the GPU by simply surrounding the code by

   !acc region
   !acc end region

with the PGI Accelerator. It would have to be a pretty big loop for it to pay off, though, since transfer to/from the GPU is very expensive.