module Algo.Spectral ( spectral ) where import Data.Vector.Unboxed as V import Data.Bits spectral :: Vector Double -> Vector Double {-# NOINLINE spectral #-} spectral us = us `seq` V.map row (V.enumFromTo 0 (n-1)) where n = V.length us row i = i `seq` V.sum (V.imap (\j u -> eval_A i j * u) us) eval_A i j = 1 / fromIntegral r where r = u + (i+1) u = t `shiftR` 1 t = n * (n+1) n = i+j