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机器学习分支之一强化学习,学习通过与环境交互进行,是一种目标导向的方法。
不告知学习者应采用行为,但其行为对于奖励惩罚,从行为后果学习。
机器人避开障碍物案例:
靠近障碍物-10分,远离障碍物+10分。
智能体自己探索获取优良奖励的各自行为,包括如下步骤:
需要对比,理解和掌握强化学习与其他机器学习的差异,在机器人中的应用前景。
强化学习元素:智能体,策略函数,值函数,模型等。
环境类型:确定,随机,完全可观测,部分可观测,离散,连续,情景序列,非情景序列,单智能体,多智能体。
强化学习平台:OpenAI Gym/Universe/DeepMind Lab/RL-Glue/Rroject Malmo/VizDoom等。
强化学习应用:教育!医疗!健康!制造业!管理!金融!细分行业:自然语言处理/计算机视觉等。
参考文献:
安装配置Anaconda/Docker/OpenAI Gym/TensorFlow。
由于涉及系统环境,版本配置各不相同,自行查阅资料配置即可。
常用命令如下:
bash/conda create/source activate/apt install/docker/pip3 install gym/universe/等。
上述全部配置完成后,测试OpenAI Gym和OpenAI Universe。
*.ipynb文档查看:ipython notebook或jupyter notebook
Gym案例:
倒立摆案例:
示例代码
import gym
env = gym.make('CartPole-v0')
env.reset()
for _ in range(1000):
    env.render()
    env.step(env.action_space.sample())关于这个代码更多内容,参考链接:
查看gym全部支持的环境。
from gym import envs
print(envs.registry.all())赛车示例:
import gym
env = gym.make('CarRacing-v0')
env.reset()
for _ in range(1000):
    env.render()
    env.step(env.action_space.sample())足式机器人:
import gym
env = gym.make('BipedalWalker-v2')
for episode in range(100):
    observation = env.reset()
    # Render the environment on each step 
    for i in range(10000):
        env.render() 
        # we choose action by sampling random action from environment's action space. Every environment has
        # some action space which contains the all possible valid actions and observations,
        action = env.action_space.sample()
        # Then for each step, we will record the observation, reward, done, info
        observation, reward, done, info = env.step(action)  
   # When done is true, we print the time steps taken for the episode and break the current episode.
    if done:
        print("{} timesteps taken for the Episode".format(i+1))
        breakflash游戏环境示例:
import gym
import universe 
import random
env = gym.make('flashgames.NeonRace-v0')
env.configure(remotes=1) 
observation_n = env.reset()
# Move left
left = [('KeyEvent', 'ArrowUp', True), ('KeyEvent', 'ArrowLeft', True),
         ('KeyEvent', 'ArrowRight', False)]
# Move right
right = [('KeyEvent', 'ArrowUp', True), ('KeyEvent', 'ArrowLeft', False),
         ('KeyEvent', 'ArrowRight', True)]
# Move forward
forward = [('KeyEvent', 'ArrowUp', True), ('KeyEvent', 'ArrowRight', False),
            ('KeyEvent', 'ArrowLeft', False), ('KeyEvent', 'n', True)]
# We use turn variable for deciding whether to turn or not
turn = 0
# We store all the rewards in rewards list
rewards = []
# we will use buffer as some kind of threshold
buffer_size = 100
# We set our initial action has forward i.e our car moves just forward without making any turns
action = forward  
while True:
    turn -= 1
    
    # Let us say initially we take no turn and move forward.
    # First, We will check the value of turn, if it is less than 0
    # then there is no necessity for turning and we just move forward
    
    if turn <= 0:
        action = forward
        turn = 0
    
    action_n = [action for ob in observation_n]
    
    # Then we use env.step() to perform an action (moving forward for now) one-time step
    
    observation_n, reward_n, done_n, info = env.step(action_n)
    
    # store the rewards in the rewards list
    rewards += [reward_n[0]]
     
    # We will generate some random number and if it is less than 0.5 then we will take right, else
    # we will take left and we will store all the rewards obtained by performing each action and
    # based on our rewards we will learn which direction is the best over several timesteps. 
    
    if len(rewards) >= buffer_size:
        mean = sum(rewards)/len(rewards)
        
        if mean == 0:
            turn = 20
            if random.random() < 0.5:
                 action = right
            else:
                action = left
        rewards = []
        
    env.render()部分测试如下(多次测试):