Eager Execution, tf.GradientTape only returns None - python-3.x

Question

I'm trying to calculate the gradient with tf.GradientTape. When I try to do it using as inputs the loss and Model.trainable_weights (tf.keras.Model) the result that returns me in an array of None. what am I doing wrong? The tensorflow version I use is 1.13.0.
The implemneted algorithm is a OnPolicy DQN(Not usual DQN) so that I don't use a target network(whihch is used as behavioural network in conventional DQN code). So, I wanted to differentiate the Error, which is defined as a minibatch MSE of Y(which is R + gamma * max_a Q(s', a')) and Q(s,a) in the code below.
import gym
import numpy as np
import tensorflow as tf
from collections import deque
# ==== import below from my repo ====
from common.wrappers import MyWrapper # just a wrapper to set a reward at the terminal state -1
from common.params import Parameters # params for training
from common.memory import ReplayBuffer # Experience Replay Buffer
tf.enable_eager_execution()
class Model(tf.keras.Model):
def __init__(self, num_action):
super(Model, self).__init__()
self.dense1 = tf.keras.layers.Dense(16, activation='relu')
self.dense2 = tf.keras.layers.Dense(16, activation='relu')
self.dense3 = tf.keras.layers.Dense(16, activation='relu')
self.pred = tf.keras.layers.Dense(num_action, activation='softmax')
def call(self, inputs):
x = self.dense1(inputs)
x = self.dense2(x)
x = self.dense3(x)
pred = self.pred(x)
return pred
class DQN:
"""
On policy DQN
"""
def __init__(self, num_action):
self.num_action = num_action
self.model = Model(num_action)
self.optimizer = tf.train.AdamOptimizer()
def predict(self, state):
return self.model(tf.convert_to_tensor(state[None, :], dtype=tf.float32)).numpy()[0]
def update(self, state, action, target):
# target: R + gamma * Q(s',a')
# calculate Q(s,a)
q_values = self.predict(state)
actions_one_hot = tf.one_hot(action, self.num_action, 1.0, 0.0)
action_probs = tf.reduce_sum(actions_one_hot * q_values, reduction_indices=-1)
# Minibatch MSE => (1/batch_size) * (R + gamma * Q(s',a') - Q(s,a))^2
loss = tf.reduce_mean(tf.squared_difference(target, action_probs))
return loss
if __name__ == '__main__':
reward_buffer = deque(maxlen=5)
env = MyWrapper(gym.make("CartPole-v0"))
replay_buffer = ReplayBuffer(5000)
params = Parameters(mode="CartPole")
agent = DQN(env.action_space.n)
for i in range(2000):
state = env.reset()
total_reward = 0
for t in range(210):
# env.render()
action = np.argmax(agent.predict(state)) # behave greedily
next_state, reward, done, info = env.step(action)
replay_buffer.add(state, action, reward, next_state, done)
total_reward += reward
state = next_state
if done:
print("Episode {0} finished after {1} timesteps".format(i, t + 1))
if i > 10:
print("Update")
with tf.GradientTape() as tape:
states, actions, rewards, next_states, dones = replay_buffer.sample(params.batch_size)
next_Q = agent.predict(next_states)
Y = rewards + params.gamma * np.max(next_Q, axis=1) * np.logical_not(dones)
loss = agent.update(states, actions, Y)
print(loss)
grads = tape.gradient(loss, agent.model.trainable_weights)
# ==== THIS RETURNS ONLY NONE ====
print(grads)
agent.optimizer.apply_gradients(zip(grads, agent.model.trainable_weights))
break
# store the episode reward
reward_buffer.append(total_reward)
# check the stopping condition
if np.mean(reward_buffer) > 195:
print("GAME OVER!!")
break
env.close()
import gym
import numpy as np
import tensorflow as tf
from collections import deque
# ==== import below from my repo ====
from common.wrappers import MyWrapper # just a wrapper to set a reward at the terminal state -1
from common.params import Parameters # params for training
from common.memory import ReplayBuffer # Experience Replay Buffer
tf.enable_eager_execution()
class Model(tf.keras.Model):
def __init__(self, num_action):
super(Model, self).__init__()
self.dense1 = tf.keras.layers.Dense(16, activation='relu')
self.dense2 = tf.keras.layers.Dense(16, activation='relu')
self.dense3 = tf.keras.layers.Dense(16, activation='relu')
self.pred = tf.keras.layers.Dense(num_action, activation='softmax')
def call(self, inputs):
x = self.dense1(inputs)
x = self.dense2(x)
x = self.dense3(x)
pred = self.pred(x)
return pred
class DQN:
"""
On policy DQN
"""
def __init__(self, num_action):
self.num_action = num_action
self.model = Model(num_action)
self.optimizer = tf.train.AdamOptimizer()
def predict(self, state):
return self.model(tf.convert_to_tensor(state[None, :], dtype=tf.float32)).numpy()[0]
def update(self, state, action, target):
# target: R + gamma * Q(s',a')
# calculate Q(s,a)
q_values = self.predict(state)
actions_one_hot = tf.one_hot(action, self.num_action, 1.0, 0.0)
action_probs = tf.reduce_sum(actions_one_hot * q_values, reduction_indices=-1)
# Minibatch MSE => (1/batch_size) * (R + gamma * Q(s',a') - Q(s,a))^2
loss = tf.reduce_mean(tf.squared_difference(target, action_probs))
return loss
if __name__ == '__main__':
reward_buffer = deque(maxlen=5)
env = MyWrapper(gym.make("CartPole-v0"))
replay_buffer = ReplayBuffer(5000)
params = Parameters(mode="CartPole")
agent = DQN(env.action_space.n)
for i in range(2000):
state = env.reset()
total_reward = 0
for t in range(210):
# env.render()
action = np.argmax(agent.predict(state)) # behave greedily
next_state, reward, done, info = env.step(action)
replay_buffer.add(state, action, reward, next_state, done)
total_reward += reward
state = next_state
if done:
print("Episode {0} finished after {1} timesteps".format(i, t + 1))
if i > 10:
print("Update")
with tf.GradientTape() as tape:
states, actions, rewards, next_states, dones = replay_buffer.sample(params.batch_size)
next_Q = agent.predict(next_states)
Y = rewards + params.gamma * np.max(next_Q, axis=1) * np.logical_not(dones)
loss = agent.update(states, actions, Y)
print(loss)
grads = tape.gradient(loss, agent.model.trainable_weights)
# ==== THIS RETURNS ONLY NONE ====
print(grads)
agent.optimizer.apply_gradients(zip(grads, agent.model.trainable_weights))
break
# store the episode reward
reward_buffer.append(total_reward)
# check the stopping condition
if np.mean(reward_buffer) > 195:
print("GAME OVER!!")
break
env.close()
import gym
import numpy as np
import tensorflow as tf
from collections import deque
# ==== import below from my repo ====
from common.wrappers import MyWrapper # just a wrapper to set a reward at the terminal state -1
from common.params import Parameters # params for training
from common.memory import ReplayBuffer # Experience Replay Buffer
tf.enable_eager_execution()
class Model(tf.keras.Model):
def __init__(self, num_action):
super(Model, self).__init__()
self.dense1 = tf.keras.layers.Dense(16, activation='relu')
self.dense2 = tf.keras.layers.Dense(16, activation='relu')
self.dense3 = tf.keras.layers.Dense(16, activation='relu')
self.pred = tf.keras.layers.Dense(num_action, activation='softmax')
def call(self, inputs):
x = self.dense1(inputs)
x = self.dense2(x)
x = self.dense3(x)
pred = self.pred(x)
return pred
class DQN:
"""
On policy DQN
"""
def __init__(self, num_action):
self.num_action = num_action
self.model = Model(num_action)
self.optimizer = tf.train.AdamOptimizer()
def predict(self, state):
return self.model(tf.convert_to_tensor(state[None, :], dtype=tf.float32)).numpy()[0]
def update(self, state, action, target):
# target: R + gamma * Q(s',a')
# calculate Q(s,a)
q_values = self.predict(state)
actions_one_hot = tf.one_hot(action, self.num_action, 1.0, 0.0)
action_probs = tf.reduce_sum(actions_one_hot * q_values, reduction_indices=-1)
# Minibatch MSE => (1/batch_size) * (R + gamma * Q(s',a') - Q(s,a))^2
loss = tf.reduce_mean(tf.squared_difference(target, action_probs))
return loss
if __name__ == '__main__':
reward_buffer = deque(maxlen=5)
env = MyWrapper(gym.make("CartPole-v0"))
replay_buffer = ReplayBuffer(5000)
params = Parameters(mode="CartPole")
agent = DQN(env.action_space.n)
for i in range(2000):
state = env.reset()
total_reward = 0
for t in range(210):
# env.render()
action = np.argmax(agent.predict(state)) # behave greedily
next_state, reward, done, info = env.step(action)
replay_buffer.add(state, action, reward, next_state, done)
total_reward += reward
state = next_state
if done:
print("Episode {0} finished after {1} timesteps".format(i, t + 1))
if i > 10:
print("Update")
with tf.GradientTape() as tape:
states, actions, rewards, next_states, dones = replay_buffer.sample(params.batch_size)
next_Q = agent.predict(next_states)
Y = rewards + params.gamma * np.max(next_Q, axis=1) * np.logical_not(dones)
loss = agent.update(states, actions, Y)
print(loss)
grads = tape.gradient(loss, agent.model.trainable_weights)
# ==== THIS RETURNS ONLY NONE ====
print(grads)
agent.optimizer.apply_gradients(zip(grads, agent.model.trainable_weights))
break
# store the episode reward
reward_buffer.append(total_reward)
# check the stopping condition
if np.mean(reward_buffer) > 195:
print("GAME OVER!!")
break
env.close()
import gym
import numpy as np
import tensorflow as tf
from collections import deque
# ==== import below from my repo ====
from common.wrappers import MyWrapper # just a wrapper to set a reward at the terminal state -1
from common.params import Parameters # params for training
from common.memory import ReplayBuffer # Experience Replay Buffer
tf.enable_eager_execution()
class Model(tf.keras.Model):
def __init__(self, num_action):
super(Model, self).__init__()
self.dense1 = tf.keras.layers.Dense(16, activation='relu')
self.dense2 = tf.keras.layers.Dense(16, activation='relu')
self.dense3 = tf.keras.layers.Dense(16, activation='relu')
self.pred = tf.keras.layers.Dense(num_action, activation='softmax')
def call(self, inputs):
x = self.dense1(inputs)
x = self.dense2(x)
x = self.dense3(x)
pred = self.pred(x)
return pred
class DQN:
"""
On policy DQN
"""
def __init__(self, num_action):
self.num_action = num_action
self.model = Model(num_action)
self.optimizer = tf.train.AdamOptimizer()
def predict(self, state):
return self.model(tf.convert_to_tensor(state[None, :], dtype=tf.float32)).numpy()[0]
def update(self, state, action, target):
# target: R + gamma * Q(s',a')
# calculate Q(s,a)
q_values = self.predict(state)
actions_one_hot = tf.one_hot(action, self.num_action, 1.0, 0.0)
action_probs = tf.reduce_sum(actions_one_hot * q_values, reduction_indices=-1)
# Minibatch MSE => (1/batch_size) * (R + gamma * Q(s',a') - Q(s,a))^2
loss = tf.reduce_mean(tf.squared_difference(target, action_probs))
return loss
if __name__ == '__main__':
reward_buffer = deque(maxlen=5)
env = MyWrapper(gym.make("CartPole-v0"))
replay_buffer = ReplayBuffer(5000)
params = Parameters(mode="CartPole")
agent = DQN(env.action_space.n)
for i in range(2000):
state = env.reset()
total_reward = 0
for t in range(210):
# env.render()
action = np.argmax(agent.predict(state)) # behave greedily
next_state, reward, done, info = env.step(action)
replay_buffer.add(state, action, reward, next_state, done)
total_reward += reward
state = next_state
if done:
print("Episode {0} finished after {1} timesteps".format(i, t + 1))
if i > 10:
print("Update")
with tf.GradientTape() as tape:
states, actions, rewards, next_states, dones = replay_buffer.sample(params.batch_size)
next_Q = agent.predict(next_states)
Y = rewards + params.gamma * np.max(next_Q, axis=1) * np.logical_not(dones)
loss = agent.update(states, actions, Y)
print(loss)
grads = tape.gradient(loss, agent.model.trainable_weights)
# ==== THIS RETURNS ONLY NONE ====
print(grads)
agent.optimizer.apply_gradients(zip(grads, agent.model.trainable_weights))
break
# store the episode reward
reward_buffer.append(total_reward)
# check the stopping condition
if np.mean(reward_buffer) > 195:
print("GAME OVER!!")
break
env.close()

Answer 1

Try to change your update function to:
def update(self, state, action, target):
# target: R + gamma * Q(s',a')
# calculate Q(s,a)
q_values = self.model(tf.convert_to_tensor(state[None, :], dtype=tf.float32))
actions_one_hot = tf.one_hot(action, self.num_action, 1.0, 0.0)
action_probs = tf.reduce_sum(actions_one_hot * q_values, reduction_indices=-1)
# Minibatch MSE => (1/batch_size) * (R + gamma * Q(s',a') - Q(s,a))^2
loss = tf.reduce_mean(tf.squared_difference(target, action_probs))
return loss
I think with the .numpy() call in the predict function the tape loses the refererence to the weights. (I've not tested my answer)