module Statistics.Distribution.Geometric
(
GeometricDistribution
, geometric
, gdSuccess
) where
import Data.Typeable (Typeable)
import qualified Statistics.Distribution as D
newtype GeometricDistribution = GD {
gdSuccess :: Double
} deriving (Eq, Read, Show, Typeable)
instance D.Distribution GeometricDistribution where
cumulative = cumulative
instance D.DiscreteDistr GeometricDistribution where
probability = probability
instance D.Mean GeometricDistribution where
mean (GD s) = 1 / s
instance D.Variance GeometricDistribution where
variance (GD s) = (1 s) / (s * s)
instance D.MaybeMean GeometricDistribution where
maybeMean = Just . D.mean
instance D.MaybeVariance GeometricDistribution where
maybeStdDev = Just . D.stdDev
maybeVariance = Just . D.variance
geometric :: Double
-> GeometricDistribution
geometric x
| x < 0 || x > 1 =
error $ "Statistics.Distribution.Geometric.geometric: probability must be in [0,1] range. Got " ++ show x
| otherwise =
GD x
probability :: GeometricDistribution -> Int -> Double
probability (GD s) n | n < 1 = 0
| otherwise = s * (1s) ** (fromIntegral n 1)
cumulative :: GeometricDistribution -> Double -> Double
cumulative (GD s) x | x < 1 = 0
| otherwise = 1 (1s) ^ (floor x :: Int)