Added example reward functions.

reward-example-prevent-zig-zag.py

@@ -0,0 +1,33 @@
+def reward_function(params):
+    '''
+    Example of penalize steering, which helps mitigate zig-zag behaviors
+    '''
+    
+    # Read input parameters
+    distance_from_center = params['distance_from_center']
+    track_width = params['track_width']
+    steering = abs(params['steering_angle']) # Only need the absolute steering angle
+
+    # Calculate 3 marks that are farther and father away from the center line
+    marker_1 = 0.1 * track_width
+    marker_2 = 0.25 * track_width
+    marker_3 = 0.5 * track_width
+
+    # Give higher reward if the car is closer to center line and vice versa
+    if distance_from_center <= marker_1:
+        reward = 1.0
+    elif distance_from_center <= marker_2:
+        reward = 0.5
+    elif distance_from_center <= marker_3:
+        reward = 0.1
+    else:
+        reward = 1e-3  # likely crashed/ close to off track
+
+    # Steering penality threshold, change the number based on your action space setting
+    ABS_STEERING_THRESHOLD = 15 
+
+    # Penalize reward if the car is steering too much
+    if steering > ABS_STEERING_THRESHOLD:
+        reward *= 0.8
+
+    return float(reward)