odeEuler

odeEuler.hs

import Data.List (mapAccumL)

showTupleWith :: (Show a, Show b) => String -> (a, b) -> String
showTupleWith sep (a, b) = show a ++ sep ++ show b

dxList :: (Enum a, Floating a) => a -> a -> [a]
dxList dx xmax = [0.0, dx..xmax]

odeEuler :: (Enum a, Floating a) => (a -> a) -> a -> a -> a -> [(a, a)]
odeEuler f yinit dx xmax = snd $ mapAccumL calc yinit $ zip xs (tail xs)
  where
    xs = dxList dx xmax
    calc y (x, x') = (y + (x' - x) * f y, (x, y))

main = do
  putStrLn $ unlines $ map (showTupleWith " ") $ odeEuler id 1.0 0.01 10.0