Gaussian elimination on lists

gausselim.hs

-- PRE: xs is sorted and not null
-- POST: r is xs without the elements that vary by
--       more than err from the median
gausselim ∷ (Num a, Ord a) ⇒ a → [a] → [a]
gausselim err xs = filter good xs
    where
      middle = xs ‼ (length xs `div` 2)
      good x = abs (x - middle) < err