Tomas Andersson
You can never go wrong with a good old fashioned hand written tail recursion when you're in doubt, they are pretty much the closest thing to for-loops there is in haskell and should be easy to grok for Imperative programmers and usually produce really fast code.
sum vect = let d = dim vect in sum' (d - 1) 0 where sum' 0 s = s + (vect @> 0) sum' index s = sum' (index - 1) (s + (vect @> index))
Do I need the strict version of sum'? Put something like sum' a b | a `seq` b `seq` False = undefined Or ghc will optimize it automatically? I always don't know when such optimization is useful.
I don't know the hmatrix api very well, but if there is a function for computing the inner product between two vectors you could always do something like the following meta code:
sum v = innerProduct v <1,1,1,1,1,1>
I just doubt the efficiency here. If v is a very large vector, I guess the allocation time of that intermediate vector [1,1..] is not small. But it is just my guess. Xiao-Yong -- c/* __o/* <\ * (__ */\ <