Simulation of van der pol equation

van_der_pol.hs

{-
van der Pol Equation
http://mathworld.wolfram.com/vanderPolEquation.html

dx/dt = y
dy/dt = m(1-x^2)y - x
-}

type R2 = (Double, Double) --(x, y)

van_der_pol :: Double -> Double -> R2 -> R2
van_der_pol mu dt (x, y) = (x+dx, y+dy)
  where
    dx = dt * y
    dy = dt * (mu*(1-x**2)*y - x)

main = do
  let result = let expansion = van_der_pol 0.5 0.01
               in  take 5000 $ iterate expansion (2,2)

  mapM_ putStrLn $ map form result
    where form (x,y) = (show x)++", "++(show y)