Euler Method about ODE

201911091817.hs

{- reference -}
-- ISBN978-4-320-01343-8
-- http://lqtmirage.hatenablog.com/entry/2017/05/29/125134

{- module to import -}

import Prelude



{- own defined structures -}

data Solution = Solution { step::Int, idvl::Double, sltn::Double }



{- own defined functions -}

methodEulerStep :: (Solution -> Double) -> Solution -> Double -> Solution
methodEulerStep arg_fncOde dataSltnCrnt stepIdvl
        = Solution {
                step = (step dataSltnCrnt) + 1,
                idvl = (idvl dataSltnCrnt) + stepIdvl,
                sltn = (sltn dataSltnCrnt) + stepIdvl * (arg_fncOde dataSltnCrnt)
        }

methodEuler :: (Solution -> Double) -> Solution -> Double -> Int -> IO ()
methodEuler arg_fncOde dataSltnCrnt stepIdvl numStepEnd = do

        Prelude.print $ [ (idvl dataSltnCrnt), (sltn dataSltnCrnt), tanh( idvl dataSltnCrnt ) ]

        if   statNumStep then methodEuler arg_fncOde dataSltnNext stepIdvl numStepEnd
        else                  return ()

        where
                dataSltnNext = methodEulerStep arg_fncOde dataSltnCrnt stepIdvl
                statNumStep  = (step dataSltnCrnt) < numStepEnd

fncOde :: Solution -> Double
fncOde dataInput = 1.0 - (sltn dataInput) * (sltn dataInput)



{- main process -}

main :: IO ()
main = do

        let init = Solution { step = 0, idvl = 0.0, sltn = 0.0 }

        methodEuler fncOde init 0.1 16

{- EOF -}