[Haskell-cafe] Efficient functional idiom for histogram
s.clover at gmail.com
Sat Aug 1 14:50:10 EDT 2009
On Aug 1, 2009, at 2:06 PM, Paul Moore wrote:
> Is the issue with random numbers just the implementation, or is it
> something inherent in the non-pure nature of a random number generator
> that makes it hard for Haskell to implement efficiently? If the
> latter, that probably makes Haskell a somewhat poor choice for
> simulation-type programs.
Well, I'm not sure of the details, but in your original
implementation, you're performing IO to pull the seed out of a ref at
every iteration. Pekka Karjalainen's doesn't do that, which probably
helps with the speedup. Along with that, Haskell has a fairly slow
random implementation. As I recall however, this is partially because
it hasn't received a great deal of optimization, but mainly because
the algorithm itself fulfills some rather strong properties -- in
particular it must be fairly statistically robust, and it must
provide a "split" function which produces generators that are
independently robust . This limits algorithm choice quite a bit.
For other random numbers, with different properties (faster, but with
tradeoffs in robustness, or ability to split, or both), you can check
hackage for at least mersenne-random and gsl-random. There may be
others that I don't recall.
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