[Haskell-cafe] Haskell, C and Matrix Multiplication

[Ketil Malde]

Blake Rain <blake.rain at gmail.com> writes:

> Here is the one in C:
>
> void multiplyM4 (float m1[4][4], float m2[4][4], float m3[4][4]) {
> m1[0][0] = m2[0][0] * m3[0][0] + m2[0][1] * m3[1][0] + m2[0][2] * m3[2][0] + m2[0][3] * m3[3][0];
> m1[0][1] = m2[0][0] * m3[0][1] + m2[0][1] * m3[1][1] + m2[0][2] * m3[2][1] + m2[0][3] * m3[3][1];
    (etc)
    :

> Some points about the C version:
    :
>   6. It's pretty fast (being written in C):
>
>      Performing  100,000,000 matrix  multiples  takes on  average
>      6.117s (with gcc -O2).
    :

> Haskell version:
>
> [foldl (+) 0 $ zipWith (*) x y | x <- m1, y <- transpose m2]
    :
>   5. It's very fast (being written in Haskell):
>
>      Performing  100,000,000  matrix  multiples takes  on  average
>      1.435s  (with ghc  -O2).

This is surprising: a C program doing an explicit list of arithmetic
operation is beaten by a factor of 4 or so by a polymorphic, lazy,
list-consuming Haskell program?  Are you sure? What am I missing? 

But, regardless of performance, I think this is a nice exposition of
some of Haskell's strengths.

-k
-- 
If I haven't seen further, it is by standing in the footprints of giants