8_2_PolicyNetwork.py

#%%
# Copyright 2016 The TensorFlow Authors. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# ==============================================================================

import numpy as np
import tensorflow as tf

import gym
env = gym.make('CartPole-v0')

env.reset()
random_episodes = 0
reward_sum = 0
while random_episodes < 10:
    env.render()
    observation, reward, done, _ = env.step(np.random.randint(0,2))
    reward_sum += reward
    if done:
        random_episodes += 1
        print("Reward for this episode was:",reward_sum)
        reward_sum = 0
        env.reset()
        
# hyperparameters
H = 50 # number of hidden layer neurons
batch_size = 25 # every how many episodes to do a param update?
learning_rate = 1e-1 # feel free to play with this to train faster or more stably.
gamma = 0.99 # discount factor for reward

D = 4 # input dimensionality        


tf.reset_default_graph()

#This defines the network as it goes from taking an observation of the environment to 
#giving a probability of chosing to the action of moving left or right.
observations = tf.placeholder(tf.float32, [None,D] , name="input_x")
W1 = tf.get_variable("W1", shape=[D, H],
           initializer=tf.contrib.layers.xavier_initializer())
layer1 = tf.nn.relu(tf.matmul(observations,W1))
W2 = tf.get_variable("W2", shape=[H, 1],
           initializer=tf.contrib.layers.xavier_initializer())
score = tf.matmul(layer1,W2)
probability = tf.nn.sigmoid(score)

#From here we define the parts of the network needed for learning a good policy.
tvars = tf.trainable_variables()
input_y = tf.placeholder(tf.float32,[None,1], name="input_y")
advantages = tf.placeholder(tf.float32,name="reward_signal")

# The loss function. This sends the weights in the direction of making actions 
# that gave good advantage (reward over time) more likely, and actions that didn't less likely.
loglik = tf.log(input_y*(input_y - probability) + (1 - input_y)*(input_y + probability))
loss = -tf.reduce_mean(loglik * advantages) 
newGrads = tf.gradients(loss,tvars)

# Once we have collected a series of gradients from multiple episodes, we apply them.
# We don't just apply gradeients after every episode in order to account for noise in the reward signal.
adam = tf.train.AdamOptimizer(learning_rate=learning_rate) # Our optimizer
W1Grad = tf.placeholder(tf.float32,name="batch_grad1") # Placeholders to send the final gradients through when we update.
W2Grad = tf.placeholder(tf.float32,name="batch_grad2")
batchGrad = [W1Grad,W2Grad]
updateGrads = adam.apply_gradients(zip(batchGrad,tvars))


def discount_rewards(r):
    """ take 1D float array of rewards and compute discounted reward """
    discounted_r = np.zeros_like(r)
    running_add = 0
    for t in reversed(range(r.size)):
        running_add = running_add * gamma + r[t]
        discounted_r[t] = running_add
    return discounted_r
    
    
    
xs,ys,drs = [],[],[]
#running_reward = None
reward_sum = 0
episode_number = 1
total_episodes = 10000
init = tf.global_variables_initializer()

# Launch the graph
with tf.Session() as sess:
    rendering = False
    sess.run(init)
    observation = env.reset() # Obtain an initial observation of the environment

    # Reset the gradient placeholder. We will collect gradients in 
    # gradBuffer until we are ready to update our policy network. 
    gradBuffer = sess.run(tvars)
    for ix,grad in enumerate(gradBuffer):
        gradBuffer[ix] = grad * 0
    
    while episode_number <= total_episodes:
        
        # Rendering the environment slows things down, 
        # so let's only look at it once our agent is doing a good job.
        if reward_sum/batch_size > 100 or rendering == True : 
            env.render()
            rendering = True
            
        # Make sure the observation is in a shape the network can handle.
        x = np.reshape(observation,[1,D])
        
        # Run the policy network and get an action to take. 
        tfprob = sess.run(probability,feed_dict={observations: x})
        action = 1 if np.random.uniform() < tfprob else 0
        
        xs.append(x) # observation
        y = 1 if action == 0 else 0 # a "fake label"
        ys.append(y)

        # step the environment and get new measurements
        observation, reward, done, info = env.step(action)
        reward_sum += reward

        drs.append(reward) # record reward (has to be done after we call step() to get reward for previous action)

        if done: 
            episode_number += 1
            # stack together all inputs, hidden states, action gradients, and rewards for this episode
            epx = np.vstack(xs)
            epy = np.vstack(ys)
            epr = np.vstack(drs)
            xs,ys,drs = [],[],[] # reset array memory

            # compute the discounted reward backwards through time
            discounted_epr = discount_rewards(epr)
            # size the rewards to be unit normal (helps control the gradient estimator variance)
            discounted_epr -= np.mean(discounted_epr)
            discounted_epr /= np.std(discounted_epr)
            
            # Get the gradient for this episode, and save it in the gradBuffer
            tGrad = sess.run(newGrads,feed_dict={observations: epx, input_y: epy, advantages: discounted_epr})
            for ix,grad in enumerate(tGrad):
                gradBuffer[ix] += grad
                
            # If we have completed enough episodes, then update the policy network with our gradients.
            if episode_number % batch_size == 0: 
                sess.run(updateGrads,feed_dict={W1Grad: gradBuffer[0],W2Grad:gradBuffer[1]})
                for ix,grad in enumerate(gradBuffer):
                    gradBuffer[ix] = grad * 0
                
                # Give a summary of how well our network is doing for each batch of episodes.
                #running_reward = reward_sum if running_reward is None else running_reward * 0.99 + reward_sum * 0.01
                print('Average reward for episode %d : %f.' % (episode_number,reward_sum/batch_size))
                
                if reward_sum/batch_size > 200: 
                    print("Task solved in",episode_number,'episodes!')
                    break
                    
                reward_sum = 0
            
            observation = env.reset()