On Thu, Nov 11, 2010 at 3:13 AM, Richard Senington
I got hold of, and looked through the paper suggested in the root of this thread “Pseudo random trees in Monte-Carlo", and based upon this I have thrown together a version of the binary tree based random number generator suggested.
I would like to point out that I do not know very much about random number generators, the underlying mathematics or any subsequent papers on this subject, this is just a very naive implementation based upon this one paper.
As a question, the following code actually generates a stream of numbers that is more random than I was expecting, if anyone can explain why I would be very interested.
What do you mean more random than you were expecting? Shouldn't they be "maximally random"? BTW, nice module. Do you want to hackage it up? If not, I will.
import System.Random
data LehmerTree = LehmerTree {nextInt :: Int, leftBranch :: LehmerTree, rightBranch :: LehmerTree}
instance Show LehmerTree where show g = "LehmerTree, current root = "++(show $ nextInt g)
mkLehmerTree :: Int->Int->Int->Int->Int->Int->LehmerTree mkLehmerTree aL aR cL cR m x0 = innerMkTree x0 where mkLeft x = (aL * x + cL) `mod` m mkRight x = (aR * x + cR) `mod` m innerMkTree x = let l = innerMkTree (mkLeft x) r = innerMkTree (mkRight x) in LehmerTree x l r
mkLehmerTreeFromRandom :: IO LehmerTree mkLehmerTreeFromRandom = do gen<-getStdGen let a:b:c:d:e:f:_ = randoms gen return $ mkLehmerTree a b c d e f
This can be pure: mkLehmerTreeFromRandom :: (RandomGen g) => g -> LehmerTree
instance RandomGen LehmerTree where next g = (fromIntegral.nextInt $ g, leftBranch g) split g = (leftBranch g, rightBranch g) genRange _ = (0, 2147483562) -- duplicate of stdRange
test :: IO() test = do gen<-mkLehmerTreeFromRandom print gen let (g1,g2) = split gen let p = take 10 $ randoms gen :: [Int] let p' = take 10 $ randoms g1 :: [Int] -- let p'' = take 10 $ randoms g2 :: [Float] print p print p' -- print p''
_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe