You can implement a reasonable split if you can fast-forward the generator.
There's no known method to fast-forward the MT, but other generators
like MRG32k3a can handle it.
-- Lennart
On Thu, Feb 26, 2009 at 12:08 PM, Bertram Felgenhauer
haskell@kudling.de wrote:
Do you think it would be feasable to replace the GHC implementation of System.Random with something like System.Random.Mersenne?
There's a problem with using the Mersenne Twister: System.Random's interface has a split method:
class RandomGen g where split :: g -> (g, g)
The Mersenne Twister is good at producing a single stream of random numbers - in fact it works by generating a whole block of random numbers in one go, then consuming the block, and only then generating the next block.
I have no idea how to implement a split method that produces independent streams. Even if I did, using split a lot would likely spoil the performance benefit of the generator.
(System.Random.Mersenne.Pure64 provides a RandomGen instance for PureMT, but it cheats:)
split = error "System.Random.Mersenne.Pure: unable to split the mersenne twister"
Bertram _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe