[Haskell-cafe] Re: [Haskell] Matrix multiplication

[David Roundy]

On Wed, Apr 23, 2008 at 05:24:20PM +0100, Sebastian Sylvan wrote:
> On Wed, Apr 23, 2008 at 5:01 PM, Tillmann Vogt <Tillmann.Vogt at rwth-aachen.de>
> wrote:
> 
> > Hi,
> >
> > I am currently experimenting with parallelizing C-programs. I have
> > therefore written a matrix vector multiplication example that needs 13
> > seconds to run (5 seconds with OpenMP). Because I like Haskell I did the
> > same in this language, but it takes about 134 seconds. Why is it so slow?
> > Does someone have an idea?
> >
> Yes, in the C version you use unboxed arrays, in the Haskell version you use
> a linked list of linked lists. Naturally the latter will take up more space,
> require more work to index, and will thrash the cache quite a bit.

In fact, I'm impressed that Haskell can come within a factor of 10, given
that it's using such a challenging data type! (I wonder if this may be due
to inefficiencies in the C code, although I haven't looked at it.)
-- 
David Roundy
Department of Physics
Oregon State University