Unbias a random generator: Difference between revisions
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randN(6) 166900 833100 16.69% |
randN(6) 166900 833100 16.69% |
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unbiased 499973 500027 50.00% |
unbiased 499973 500027 50.00% |
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</pre> |
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=={{header|Haskell}}== |
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Crappy implementation using <code>IO</code> |
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<lang haskell>import Control.Monad |
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import Random |
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import Data.IORef |
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import Text.Printf |
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randN :: Integer -> IO Bool |
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randN n = randomRIO (1,n) >>= return . (== 1) |
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unbiased :: Integer -> IO Bool |
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unbiased n = do |
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a <- randN n |
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b <- randN n |
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if a /= b then return a else unbiased n |
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main :: IO () |
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main = forM_ [3..6] $ \n -> do |
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cb <- newIORef 0 |
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cu <- newIORef 0 |
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replicateM_ 50000 $ do |
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b <- randN n |
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u <- unbiased n |
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when b $ modifyIORef cb (+ 1) |
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when u $ modifyIORef cu (+ 1) |
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tb <- readIORef cb |
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tu <- readIORef cu |
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printf "%d: %5.2f%% %5.2f%%\n" n |
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(100 * fromIntegral tb / fromIntegral trials :: Double) |
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(100 * fromIntegral tu / fromIntegral trials :: Double) |
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where trials = 50000</lang> |
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Output: |
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<pre> |
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3: 33.72% 50.08% |
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4: 25.26% 50.15% |
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5: 19.99% 50.07% |
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6: 16.67% 50.10% |
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</pre> |
</pre> |
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