Created
April 19, 2012 12:04
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import System.Environment (getArgs) | |
import System.Random | |
import Control.Monad (liftM) | |
import Data.Array.Unboxed | |
import qualified Data.Vector as V | |
import qualified Data.Vector.Unboxed as VU | |
configs :: Int -> [[Char]] -- List of configurations | |
configs n = V.toList $ V.take (3^n) $ V.fromList $ iterate nextConfig $ replicate n '0' | |
where nextConfig ('0':xs) = '1':xs | |
nextConfig ('1':xs) = '2':xs | |
nextConfig ('2':xs) = '0':(nextConfig xs) | |
normals :: [Double] -> [Double] -- I.i.d. N(0,1) random variables | |
normals (r1:r2:rs) = (sqrt (-2 * log r1) * cos (2*pi * r2)) : (normals rs) | |
data Stats = Stats { n0 :: !Int, n1 :: !Int, n2 :: !Int, ff :: !Double } | |
curieWeiss :: [Double] -> [Char] -> (Int,Double) -- Field -> Config -> RF Hamiltonian | |
curieWeiss f xs = (n1-n2, exp(field-det)) | |
where Stats n0 n1 n2 ff = VU.foldl acc (Stats 0 0 0 0) $ VU.zip (VU.fromList xs) (VU.fromList f) | |
acc s@(Stats k0 _ _ uu) ('0',u) = s { n0 = k0 + 1, ff = uu + u } | |
acc s@(Stats _ k1 _ uu) ('1',u) = s { n1 = k1 + 1, ff = uu - 0.5*u } | |
acc s@(Stats _ _ k2 uu) ('2',u) = s { n2 = k2 + 1, ff = uu - 0.5*u } | |
field = (fromIntegral $ n0+n1+n2) * ff | |
det = fromIntegral $ 3 * (n0*n1 + n0*n2 + n1*n2) | |
run :: [Double] -> Int -> UArray Int Double -- Field -> n -> partition function, fractioned by n1-n2 | |
run f n = accumArray (+) 0.0 (-n,n) $ map (curieWeiss f) $ configs n | |
main :: IO () | |
main = do n <- liftM (read . head) getArgs | |
f <- liftM (take n . normals . randoms) getStdGen | |
mapM_ p $ assocs $ run (map sign f) n | |
where p (i,x) = putStrLn $ (show i) ++ " " ++ (show $ - log x) | |
sign x = if x>0 then 1.0 else -1.0 |
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