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# AWS DeepRacer 奖励功能示例
<a name="deepracer-reward-function-examples"></a>

以下列出了 AWS DeepRacer 奖励功能的一些示例。

**Topics**
+ [示例 1：在计时赛中紧贴中心线行驶](#deepracer-reward-function-example-0)
+ [示例 2：在计时赛中保持在界内](#deepracer-reward-function-example-1)
+ [示例 3：在计时赛中防止之字形行驶](#deepracer-reward-function-example-2)
+ [示例 4：保持在一条车道而不撞到静止障碍物或移动的车辆](#deepracer-reward-function-example-3)

## 示例 1：在计时赛中紧贴中心线行驶
<a name="deepracer-reward-function-example-0"></a>

 此示例确定代理距中心线的距离，如果代理靠近赛道的中心，则提供更高的奖励，鼓励代理紧贴中心线行驶。

```
def reward_function(params):
    '''
    Example of rewarding the agent to follow center line
    '''
    
    # Read input parameters
    track_width = params['track_width']
    distance_from_center = params['distance_from_center']

    # Calculate 3 markers that are increasingly further 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
    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

    return reward
```

## 示例 2：在计时赛中保持在界内
<a name="deepracer-reward-function-example-1"></a>

 此示例在代理保持在界内时给予更高的奖励，让代理弄清楚完成一圈的最佳路线。编程和理解很容易，但可能需要更长的时间才能融合。

```
def reward_function(params):
    '''
    Example of rewarding the agent to stay inside the two borders of the track
    '''
    
    # Read input parameters
    all_wheels_on_track = params['all_wheels_on_track']
    distance_from_center = params['distance_from_center']
    track_width = params['track_width']
    
    # Give a very low reward by default
    reward = 1e-3

    # Give a high reward if no wheels go off the track and 
    # the car is somewhere in between the track borders 
    if all_wheels_on_track and (0.5*track_width - distance_from_center) >= 0.05:
        reward = 1.0

    # Always return a float value
    return reward
```

## 示例 3：在计时赛中防止之字形行驶
<a name="deepracer-reward-function-example-2"></a>

 此示例奖励代理紧贴中心线行驶，但如果转向角太大，则会受到惩罚（减少奖励），这有助于防止之字形行驶。代理在模拟器中学习了平稳驾驶，在部署到实际车辆时倾向于保持相同的行为。

```
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']
    abs_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 abs_steering > ABS_STEERING_THRESHOLD:
        reward *= 0.8

    return float(reward)
```

## 示例 4：保持在一条车道而不撞到静止障碍物或移动的车辆
<a name="deepracer-reward-function-example-3"></a>

 

此奖励函数奖励代理保持在赛道边界内，如果代理太靠近前面的物体，则会受到惩罚。代理可变道以避免撞车。总奖励是奖励和惩罚的加权总和。此示例在惩罚方面的权重更高，以避免撞车。尝试使用不同的平均权重，以针对不同的行为结果进行训练。

 

```
import math
def reward_function(params):
    '''
    Example of rewarding the agent to stay inside two borders
    and penalizing getting too close to the objects in front
    '''
    all_wheels_on_track = params['all_wheels_on_track']
    distance_from_center = params['distance_from_center']
    track_width = params['track_width']
    objects_location = params['objects_location']
    agent_x = params['x']
    agent_y = params['y']
    _, next_object_index = params['closest_objects']
    objects_left_of_center = params['objects_left_of_center']
    is_left_of_center = params['is_left_of_center']
    # Initialize reward with a small number but not zero
    # because zero means off-track or crashed
    reward = 1e-3
    # Reward if the agent stays inside the two borders of the track
    if all_wheels_on_track and (0.5 * track_width - distance_from_center) >= 0.05:
        reward_lane = 1.0
    else:
        reward_lane = 1e-3
    # Penalize if the agent is too close to the next object
    reward_avoid = 1.0
    # Distance to the next object
    next_object_loc = objects_location[next_object_index]
    distance_closest_object = math.sqrt((agent_x - next_object_loc[0])**2 + (agent_y - next_object_loc[1])**2)
    # Decide if the agent and the next object is on the same lane
    is_same_lane = objects_left_of_center[next_object_index] == is_left_of_center
    if is_same_lane:
        if 0.5 <= distance_closest_object < 0.8:
            reward_avoid *= 0.5
        elif 0.3 <= distance_closest_object < 0.5:
            reward_avoid *= 0.2
        elif distance_closest_object < 0.3:
            reward_avoid = 1e-3  # Likely crashed
    # Calculate reward by putting different weights on
    # the two aspects above
    reward += 1.0 * reward_lane + 4.0 * reward_avoid
    return reward
```