Solution for math problem
| -- Haskell version of formulae from | |
| -- https://youtu.be/4FNCIYD8HdA | |
| import Control.Monad (join) | |
| import Data.Ratio | |
| oneS :: [Rational] | |
| oneS = join $ repeat [1, (-1)] | |
| pSum :: Int -> Rational | |
| pSum 1 = 1 | |
| pSum 2 = 2 | |
| pSum 3 = 3 | |
| pSum n = sum (zipWith (*) oneS (map (\k -> pSum (n - k) * eSum k) [1 .. (n - 1)])) + fromIntegral n * (oneS !! n) * eSum n | |
| eSum :: Int -> Rational | |
| eSum 0 = 1 | |
| eSum 1 = 1 | |
| eSum n | n > 3 = 0 | |
| eSum n = sum (zipWith (*) oneS (map (\k -> pSum k * eSum (n - k)) [1 .. n])) / fromIntegral n | |
| -- now try | |
| -- pSum 4 | |
| -- pSum 5 |
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