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policy_value_net_tensorflow.py
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policy_value_net_tensorflow.py
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# -*- coding: utf-8 -*-
"""
An implementation of the policyValueNet in Tensorflow
Tested in Tensorflow 1.4 and 1.5
@author: Xiang Zhong
"""
import numpy as np
import tensorflow as tf
class PolicyValueNet():
def __init__(self, board_width, board_height, model_file=None):
self.board_width = board_width
self.board_height = board_height
# Define the tensorflow neural network
# 1. Input:
self.input_states = tf.placeholder(
tf.float32, shape=[None, 4, board_height, board_width])
self.input_state = tf.transpose(self.input_states, [0, 2, 3, 1])
# 2. Common Networks Layers
self.conv1 = tf.layers.conv2d(inputs=self.input_state,
filters=32, kernel_size=[3, 3],
padding="same", data_format="channels_last",
activation=tf.nn.relu)
self.conv2 = tf.layers.conv2d(inputs=self.conv1, filters=64,
kernel_size=[3, 3], padding="same",
data_format="channels_last",
activation=tf.nn.relu)
self.conv3 = tf.layers.conv2d(inputs=self.conv2, filters=128,
kernel_size=[3, 3], padding="same",
data_format="channels_last",
activation=tf.nn.relu)
# 3-1 Action Networks
self.action_conv = tf.layers.conv2d(inputs=self.conv3, filters=4,
kernel_size=[1, 1], padding="same",
data_format="channels_last",
activation=tf.nn.relu)
# Flatten the tensor
self.action_conv_flat = tf.reshape(
self.action_conv, [-1, 4 * board_height * board_width])
# 3-2 Full connected layer, the output is the log probability of moves
# on each slot on the board
self.action_fc = tf.layers.dense(inputs=self.action_conv_flat,
units=board_height * board_width,
activation=tf.nn.log_softmax)
# 4 Evaluation Networks
self.evaluation_conv = tf.layers.conv2d(inputs=self.conv3, filters=2,
kernel_size=[1, 1],
padding="same",
data_format="channels_last",
activation=tf.nn.relu)
self.evaluation_conv_flat = tf.reshape(
self.evaluation_conv, [-1, 2 * board_height * board_width])
self.evaluation_fc1 = tf.layers.dense(inputs=self.evaluation_conv_flat,
units=64, activation=tf.nn.relu)
# output the score of evaluation on current state
self.evaluation_fc2 = tf.layers.dense(inputs=self.evaluation_fc1,
units=1, activation=tf.nn.tanh)
# Define the Loss function
# 1. Label: the array containing if the game wins or not for each state
self.labels = tf.placeholder(tf.float32, shape=[None, 1])
# 2. Predictions: the array containing the evaluation score of each state
# which is self.evaluation_fc2
# 3-1. Value Loss function
self.value_loss = tf.losses.mean_squared_error(self.labels,
self.evaluation_fc2)
# 3-2. Policy Loss function
self.mcts_probs = tf.placeholder(
tf.float32, shape=[None, board_height * board_width])
self.policy_loss = tf.negative(tf.reduce_mean(
tf.reduce_sum(tf.multiply(self.mcts_probs, self.action_fc), 1)))
# 3-3. L2 penalty (regularization)
l2_penalty_beta = 1e-4
vars = tf.trainable_variables()
l2_penalty = l2_penalty_beta * tf.add_n(
[tf.nn.l2_loss(v) for v in vars if 'bias' not in v.name.lower()])
# 3-4 Add up to be the Loss function
self.loss = self.value_loss + self.policy_loss + l2_penalty
# Define the optimizer we use for training
self.learning_rate = tf.placeholder(tf.float32)
self.optimizer = tf.train.AdamOptimizer(
learning_rate=self.learning_rate).minimize(self.loss)
# Make a session
self.session = tf.Session()
# calc policy entropy, for monitoring only
self.entropy = tf.negative(tf.reduce_mean(
tf.reduce_sum(tf.exp(self.action_fc) * self.action_fc, 1)))
# Initialize variables
init = tf.global_variables_initializer()
self.session.run(init)
# For saving and restoring
self.saver = tf.train.Saver()
if model_file is not None:
self.restore_model(model_file)
def policy_value(self, state_batch):
"""
input: a batch of states
output: a batch of action probabilities and state values
"""
log_act_probs, value = self.session.run(
[self.action_fc, self.evaluation_fc2],
feed_dict={self.input_states: state_batch}
)
act_probs = np.exp(log_act_probs)
return act_probs, value
def policy_value_fn(self, board):
"""
input: board
output: a list of (action, probability) tuples for each available
action and the score of the board state
"""
legal_positions = board.availables
current_state = np.ascontiguousarray(board.current_state().reshape(
-1, 4, self.board_width, self.board_height))
act_probs, value = self.policy_value(current_state)
act_probs = zip(legal_positions, act_probs[0][legal_positions])
return act_probs, value
def train_step(self, state_batch, mcts_probs, winner_batch, lr):
"""perform a training step"""
winner_batch = np.reshape(winner_batch, (-1, 1))
loss, entropy, _ = self.session.run(
[self.loss, self.entropy, self.optimizer],
feed_dict={self.input_states: state_batch,
self.mcts_probs: mcts_probs,
self.labels: winner_batch,
self.learning_rate: lr})
return loss, entropy
def save_model(self, model_path):
self.saver.save(self.session, model_path)
def restore_model(self, model_path):
self.saver.restore(self.session, model_path)