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ppo_tf2_cartpole.py
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ppo_tf2_cartpole.py
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import tensorflow as tf
from tensorflow import keras
import tensorflow_probability as tfp
import numpy as np
import gym
import datetime as dt
STORE_PATH = 'C:\\Users\\andre\\TensorBoard\\PPOCartpole'
CRITIC_LOSS_WEIGHT = 0.5
ENTROPY_LOSS_WEIGHT = 0.01
ENT_DISCOUNT_RATE = 0.995
BATCH_SIZE = 64
GAMMA = 0.99
CLIP_VALUE = 0.2
LR = 0.001
NUM_TRAIN_EPOCHS = 10
env = gym.make("CartPole-v0")
state_size = 4
num_actions = env.action_space.n
ent_discount_val = ENTROPY_LOSS_WEIGHT
class Model(keras.Model):
def __init__(self, num_actions):
super().__init__()
self.num_actions = num_actions
self.dense1 = keras.layers.Dense(64, activation='relu',
kernel_initializer=keras.initializers.he_normal())
self.dense2 = keras.layers.Dense(64, activation='relu',
kernel_initializer=keras.initializers.he_normal())
self.value = keras.layers.Dense(1)
self.policy_logits = keras.layers.Dense(num_actions)
def call(self, inputs):
x = self.dense1(inputs)
x = self.dense2(x)
return self.value(x), self.policy_logits(x)
def action_value(self, state):
value, logits = self.predict_on_batch(state)
dist = tfp.distributions.Categorical(logits=logits)
action = dist.sample()
return action, value
def critic_loss(discounted_rewards, value_est):
return tf.cast(tf.reduce_mean(keras.losses.mean_squared_error(discounted_rewards, value_est)) * CRITIC_LOSS_WEIGHT,
tf.float32)
def entropy_loss(policy_logits, ent_discount_val):
probs = tf.nn.softmax(policy_logits)
entropy_loss = -tf.reduce_mean(keras.losses.categorical_crossentropy(probs, probs))
return entropy_loss * ent_discount_val
def actor_loss(advantages, old_probs, action_inds, policy_logits):
probs = tf.nn.softmax(policy_logits)
new_probs = tf.gather_nd(probs, action_inds)
ratio = new_probs / old_probs
policy_loss = -tf.reduce_mean(tf.math.minimum(
ratio * advantages,
tf.clip_by_value(ratio, 1.0 - CLIP_VALUE, 1.0 + CLIP_VALUE) * advantages
))
return policy_loss
def train_model(action_inds, old_probs, states, advantages, discounted_rewards, optimizer, ent_discount_val):
with tf.GradientTape() as tape:
values, policy_logits = model.call(tf.stack(states))
act_loss = actor_loss(advantages, old_probs, action_inds, policy_logits)
ent_loss = entropy_loss(policy_logits, ent_discount_val)
c_loss = critic_loss(discounted_rewards, values)
tot_loss = act_loss + ent_loss + c_loss
grads = tape.gradient(tot_loss, model.trainable_variables)
optimizer.apply_gradients(zip(grads, model.trainable_variables))
return tot_loss, c_loss, act_loss, ent_loss
def get_advantages(rewards, dones, values, next_value):
discounted_rewards = np.array(rewards + [next_value[0]])
for t in reversed(range(len(rewards))):
discounted_rewards[t] = rewards[t] + GAMMA * discounted_rewards[t+1] * (1-dones[t])
discounted_rewards = discounted_rewards[:-1]
# advantages are bootstrapped discounted rewards - values, using Bellman's equation
advantages = discounted_rewards - np.stack(values)[:, 0]
# standardise advantages
advantages -= np.mean(advantages)
advantages /= (np.std(advantages) + 1e-10)
# standardise rewards too
discounted_rewards -= np.mean(discounted_rewards)
discounted_rewards /= (np.std(discounted_rewards) + 1e-8)
return discounted_rewards, advantages
model = Model(num_actions)
optimizer = keras.optimizers.Adam(learning_rate=LR)
train_writer = tf.summary.create_file_writer(STORE_PATH + f"/PPO-CartPole_{dt.datetime.now().strftime('%d%m%Y%H%M')}")
num_steps = 10000000
episode_reward_sum = 0
state = env.reset()
episode = 1
total_loss = None
for step in range(num_steps):
rewards = []
actions = []
values = []
states = []
dones = []
probs = []
for _ in range(BATCH_SIZE):
_, policy_logits = model(state.reshape(1, -1))
action, value = model.action_value(state.reshape(1, -1))
new_state, reward, done, _ = env.step(action.numpy()[0])
actions.append(action)
values.append(value[0])
states.append(state)
dones.append(done)
probs.append(policy_logits)
episode_reward_sum += reward
state = new_state
if done:
rewards.append(0.0)
state = env.reset()
if total_loss is not None:
print(f"Episode: {episode}, latest episode reward: {episode_reward_sum}, "
f"total loss: {np.mean(total_loss)}, critic loss: {np.mean(c_loss)}, "
f"actor loss: {np.mean(act_loss)}, entropy loss {np.mean(ent_loss)}")
with train_writer.as_default():
tf.summary.scalar('rewards', episode_reward_sum, episode)
episode_reward_sum = 0
episode += 1
else:
rewards.append(reward)
_, next_value = model.action_value(state.reshape(1, -1))
discounted_rewards, advantages = get_advantages(rewards, dones, values, next_value[0])
actions = tf.squeeze(tf.stack(actions))
probs = tf.nn.softmax(tf.squeeze(tf.stack(probs)))
action_inds = tf.stack([tf.range(0, actions.shape[0]), tf.cast(actions, tf.int32)], axis=1)
total_loss = np.zeros((NUM_TRAIN_EPOCHS))
act_loss = np.zeros((NUM_TRAIN_EPOCHS))
c_loss = np.zeros(((NUM_TRAIN_EPOCHS)))
ent_loss = np.zeros((NUM_TRAIN_EPOCHS))
for epoch in range(NUM_TRAIN_EPOCHS):
loss_tuple = train_model(action_inds, tf.gather_nd(probs, action_inds),
states, advantages, discounted_rewards, optimizer,
ent_discount_val)
total_loss[epoch] = loss_tuple[0]
c_loss[epoch] = loss_tuple[1]
act_loss[epoch] = loss_tuple[2]
ent_loss[epoch] = loss_tuple[3]
ent_discount_val *= ENT_DISCOUNT_RATE
with train_writer.as_default():
tf.summary.scalar('tot_loss', np.mean(total_loss), step)
tf.summary.scalar('critic_loss', np.mean(c_loss), step)
tf.summary.scalar('actor_loss', np.mean(act_loss), step)
tf.summary.scalar('entropy_loss', np.mean(ent_loss), step)