{-# LANGUAGE NoImplicitPrelude , GeneralizedNewtypeDeriving , PatternGuards #-} -- | An interpretation of species as exponential generating functions, -- which count labelled structures. module Math.Combinatorics.Species.Labelled ( labelled ) where import Math.Combinatorics.Species.Types import Math.Combinatorics.Species.Class import qualified MathObj.PowerSeries as PS import qualified MathObj.FactoredRational as FQ import NumericPrelude import PreludeBase hiding (cycle) facts :: [Integer] facts = 1 : zipWith (*) [1..] facts instance Species EGF where singleton = egfFromCoeffs [0,1] set = egfFromCoeffs (map (LR . (1%)) facts) cycle = egfFromCoeffs (0 : map (LR . (1%)) [1..]) o = liftEGF2 PS.compose cartesian = liftEGF2 . PS.lift2 $ \xs ys -> zipWith3 mult xs ys (map fromIntegral facts) where mult x y z = x * y * z fcomp = liftEGF2 . PS.lift2 $ \fs gs -> map (\(n,gn) -> let gn' = numerator . unLR $ gn in (fs `safeIndex` gn') * LR (toRational (FQ.factorial gn' / FQ.factorial n))) (zip [0..] $ zipWith (*) (map fromIntegral facts) gs) where safeIndex [] _ = 0 safeIndex (x:_) 0 = x safeIndex (_:xs) n = safeIndex xs (n-1) ofSize s p = (liftEGF . PS.lift1 $ filterCoeffs p) s ofSizeExactly s n = (liftEGF . PS.lift1 $ selectIndex n) s -- | Extract the coefficients of an exponential generating function as -- a list of Integers. Since 'EGF' is an instance of -- 'Species', the idea is that 'labelled' can be applied directly to -- an expression of the Species DSL. In particular, @labelled s !! -- n@ is the number of labelled s-structures on an underlying set of -- size n. For example: -- -- > > take 10 $ labelled octopi -- > [0,1,3,14,90,744,7560,91440,1285200,20603520] -- -- gives the number of labelled octopi on 0, 1, 2, 3, ... 9 elements. labelled :: EGF -> [Integer] labelled (EGF f) = map numerator . zipWith (*) (map fromInteger facts) . map unLR $ PS.coeffs f -- A previous version of this module used an EGF library which -- explicitly computed with EGF's. However, it turned out to be much -- slower than just computing explicitly with normal power series and -- zipping/unzipping with factorial denominators as necessary, which -- is the current approach. -- -- instance Species (EGF.T Integer) where -- singleton = EGF.fromCoeffs [0,1] -- set = EGF.fromCoeffs $ repeat 1 -- list = EGF.fromCoeffs facts -- o = EGF.compose -- nonEmpty (EGF.Cons (_:xs)) = EGF.Cons (0:xs) -- nonEmpty x = x -- -- labelled :: EGF.T Integer -> [Integer] -- labelled = EGF.coeffs --