# statistics / Statistics / Distribution / Uniform.hs

The default branch has multiple heads

 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77``` ```{-# LANGUAGE DeriveDataTypeable, DeriveGeneric #-} -- | -- Module : Statistics.Distribution.Uniform -- Copyright : (c) 2011 Aleksey Khudyakov -- License : BSD3 -- -- Maintainer : bos@serpentine.com -- Stability : experimental -- Portability : portable -- -- Variate distributed uniformly in the interval. module Statistics.Distribution.Uniform ( UniformDistribution -- * Constructors , uniformDistr -- ** Accessors , uniformA , uniformB ) where import Data.Binary (Binary) import Data.Data (Data, Typeable) import GHC.Generics (Generic) import qualified Statistics.Distribution as D import qualified System.Random.MWC as MWC -- | Uniform distribution from A to B data UniformDistribution = UniformDistribution { uniformA :: {-# UNPACK #-} !Double -- ^ Low boundary of distribution , uniformB :: {-# UNPACK #-} !Double -- ^ Upper boundary of distribution } deriving (Eq, Read, Show, Typeable, Data, Generic) instance Binary UniformDistribution -- | Create uniform distribution. uniformDistr :: Double -> Double -> UniformDistribution uniformDistr a b | b < a = uniformDistr b a | a < b = UniformDistribution a b | otherwise = error "Statistics.Distribution.Uniform.uniform: wrong parameters" -- NOTE: failure is in default branch to guard againist NaNs. instance D.Distribution UniformDistribution where cumulative (UniformDistribution a b) x | x < a = 0 | x > b = 1 | otherwise = (x - a) / (b - a) instance D.ContDistr UniformDistribution where density (UniformDistribution a b) x | x < a = 0 | x > b = 0 | otherwise = 1 / (b - a) quantile (UniformDistribution a b) p | p >= 0 && p <= 1 = a + (b - a) * p | otherwise = error \$ "Statistics.Distribution.Uniform.quantile: p must be in [0,1] range. Got: "++show p instance D.Mean UniformDistribution where mean (UniformDistribution a b) = 0.5 * (a + b) instance D.Variance UniformDistribution where -- NOTE: 1/sqrt 12 is not constant folded (#4101) so it's written as -- numerical constant. (Also FIXME!) stdDev (UniformDistribution a b) = 0.2886751345948129 * (b - a) variance (UniformDistribution a b) = d * d / 12 where d = b - a instance D.MaybeMean UniformDistribution where maybeMean = Just . D.mean instance D.MaybeVariance UniformDistribution where maybeStdDev = Just . D.stdDev instance D.ContGen UniformDistribution where genContVar (UniformDistribution a b) gen = MWC.uniformR (a,b) gen ```