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Description | ||||||||||||

Tested with: GHC 6.8.2 Generate pseudo-random numbers using the SIMD-oriented Fast Mersenne Twister(SFMT)
pseudorandom number generator. This is a This library may be compiled with the '-f use_sse2' or '-f use_altivec' flags to configure, on intel and powerpc machines respectively, to enable high performance vector instructions to be used. This typically results in a 2-3x speedup in generation time. This will work for newer intel chips such as Pentium 4s, and Core, Core2* chips. | ||||||||||||

Synopsis | ||||||||||||

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The random number generator | ||||||||||||

data MTGen | ||||||||||||

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Initialising the generator | ||||||||||||

newMTGen :: Maybe Word32 -> IO MTGen | ||||||||||||

Return an initialised SIMD Fast Mersenne Twister. The generator is initialised based on the clock time, if Nothing is passed as a seed. For deterministic behaviour, pass an explicit seed. Due to the current SFMT library being vastly impure, currently only a single generator is allowed per-program. Attempts to reinitialise it will fail. | ||||||||||||

Random values of various types | ||||||||||||

Instances MTRandom for Word, Word64, Word32, Word16, Word8 all return, quickly, a random inhabintant of that type, in its full range. Similarly for Int types. Int and Word will be 32 bits on a 32 bit machine, and 64 on a 64 bit machine. The double precision will be 32 bits on a 32 bit machine, and 53 on a 64 bit machine. The MTRandom instance for Double returns a Double in the interval [0,1). The Bool instance takes the lower bit off a random word. | ||||||||||||

class MTRandom a where | ||||||||||||

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Miscellaneous | ||||||||||||

version :: String | ||||||||||||

Returns the identification string for the SMFT version. The string shows the word size, the Mersenne exponent, and all parameters of this generator. | ||||||||||||

An example, calculation of pi via a monte carlo method: import System.Random.Mersenne import System.Environment We'll roll the dice lim times, main = do [lim] <- mapM readIO =<< getArgs Now, define a loop that runs this many times, plotting a x and y position, then working out if its in and outside the circle. The ratio of inside/total points at then gives us an approximation of pi. let go :: Int -> Int -> IO Double go throws ins | throws >= lim = return ((4 * fromIntegral ins) / (fromIntegral throws)) | otherwise = do x <- random g :: IO Double y <- random g :: IO Double if x * x + y * y < 1 then go (throws+1) $! ins + 1 else go (throws+1) ins Compiling this, '-fexcess-precision', for accurate Doubles, $ ghc -fexcess-precision -fvia-C pi.hs -o pi $ ./pi 10000000 3.1417304 | ||||||||||||

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