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module Probability.Distribution.Multinomial where
import Probability.Random
import MCMC
import Probability.Distribution.Binomial
foreign import bpcall "Distribution:multinomial_density" builtin_multinomial_density :: Int -> EVector Double -> EVector Int -> LogDouble
data Multinomial = Multinomial Int [Double]
instance Dist Multinomial where
type Result Multinomial = [Int]
dist_name _ = "multinomial"
instance IOSampleable Multinomial where
sampleIO (Multinomial n ps) = sampleIO $ sample_multinomial n ps
instance HasPdf Multinomial where
pdf (Multinomial n ps) ks | length ks /= n = 0
| otherwise = multinomial_density n ps ks
instance HasAnnotatedPdf Multinomial where
annotated_densities dist = make_densities $ pdf dist
instance Sampleable Multinomial where
sample (Multinomial n ps) = sample_multinomial n ps
multinomial_density n ps ks = builtin_multinomial_density n ps' ks'
where ps' = toVector ps
ks' = toVector ks
sample_multinomial n [] = return []
sample_multinomial n (p:ps) = do
let normalize xs = map (/sum xs) xs
m <- sample $ binomial n p
ms <- sample_multinomial (n-m) (normalize ps)
return (m:ms)
multinomial ps = Multinomial (length ps) ps
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