[Haskell-cafe] "sum" in hmatrix and blas?
toman144 at student.liu.se
Sun Jun 8 08:54:17 EDT 2008
Den Sunday 08 June 2008 00.45.01 skrev Xiao-Yong Jin:
> Any delightful idea to convert my mind from a C shaped one
> to a Haskell shaped one?
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))
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>
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