Data commit

Task/Animate-a-pendulum/Haskell/animate-a-pendulum-1.hs

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+import Graphics.HGL.Draw.Monad (Graphic, )
+import Graphics.HGL.Draw.Picture
+import Graphics.HGL.Utils
+import Graphics.HGL.Window
+import Graphics.HGL.Run
+
+import Control.Exception (bracket, )
+import Control.Arrow
+
+toInt = fromIntegral.round
+
+pendulum = runGraphics $
+  bracket
+    (openWindowEx "Pendulum animation task" Nothing (600,400) DoubleBuffered (Just 30))
+    closeWindow
+    (\w -> mapM_ ((\ g -> setGraphic w g >> getWindowTick w).
+                    (\ (x, y) -> overGraphic (line (300, 0) (x, y))
+                                    (ellipse (x - 12, y + 12) (x + 12, y - 12)) )) pts)
+ where
+    dt = 1/30
+    t = - pi/4
+    l = 1
+    g = 9.812
+    nextAVT (a,v,t) = (a', v', t + v' * dt) where
+        a' = - (g / l) * sin t
+        v' = v + a' * dt
+    pts = map (\(_,t,_) -> (toInt.(300+).(300*).cos &&& toInt. (300*).sin) (pi/2+0.6*t) )
+        $ iterate nextAVT (- (g / l) * sin t, t, 0)

Task/Animate-a-pendulum/Haskell/animate-a-pendulum-2.hs

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+import Graphics.Gloss
+
+-- Initial conditions
+g_  = (-9.8)        :: Float    --Gravity acceleration
+v_0 = 0             :: Float    --Initial tangential speed
+a_0 = 0 / 180 * pi  :: Float    --Initial angle
+dt  = 0.01          :: Float    --Time step
+t_f = 15            :: Float    --Final time for data logging
+l_  = 200           :: Float    --Rod length
+
+-- Define a type to represent the pendulum:
+type Pendulum = (Float, Float, Float) -- (rod length, tangential speed, angle)
+
+-- Pendulum's initial state
+initialstate :: Pendulum
+initialstate = (l_, v_0, a_0)
+
+-- Step funtion: update pendulum to new position
+movePendulum :: Float -> Pendulum -> Pendulum
+movePendulum dt (l,v,a) = ( l , v_2 , a + v_2 / l * dt*10 )
+    where   v_2 = v + g_ * (cos a) * dt
+
+-- Convert from Pendulum to [Picture] for display
+renderPendulum :: Pendulum -> [Picture]
+renderPendulum (l,v,a) = map (uncurry Translate newOrigin)
+                            [ Line    [ ( 0 , 0 ) , ( l * (cos a), l * (sin a) ) ]
+                            , polygon [ ( 0 , 0 ) , ( -5 , 8.66 ) , ( 5 , 8.66 ) ]
+                            , Translate ( l * (cos a)) (l * (sin a)) (circleSolid (0.04*l_))
+                            , Translate (-1.1*l) (-1.3*l) (Scale 0.1 0.1 (Text currSpeed))
+                            , Translate (-1.1*l) (-1.3*l + 20) (Scale 0.1 0.1 (Text currAngle))
+                            ]
+    where   currSpeed = "Speed (pixels/s) = " ++ (show v)
+            currAngle = "Angle (deg) = " ++ (show ( 90 + a / pi * 180 ) )
+
+-- New origin to beter display the animation
+newOrigin = (0, l_ / 2)
+
+-- Calcule a proper window size (for angles between 0 and -pi)
+windowSize :: (Int, Int)
+windowSize = ( 300 + 2 * round (snd newOrigin)
+             , 200 + 2 * round (snd newOrigin) )
+
+-- Run simulation
+main :: IO ()
+main = do   --plotOnGNU
+            simulate window background fps initialstate render update
+                where   window      = InWindow "Animate a pendulum" windowSize (40, 40)
+                        background  = white
+                        fps         = round (1/dt)
+                        render xs   = pictures $ renderPendulum xs
+                        update _    = movePendulum