qtable.py

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"""
Example of Q-table learning with a simple discretized 1-pendulum environment.
"""
 
import signal
import time
 
import matplotlib.pyplot as plt
import numpy as np
from dpendulum import DPendulum
 
 
RANDOM_SEED = int((time.time() % 10) * 1000)
print("Seed = %d" % RANDOM_SEED)
np.random.seed(RANDOM_SEED)
 
 
NEPISODES = 500  # Number of training episodes
NSTEPS = 50  # Max episode length
LEARNING_RATE = 0.85  #
DECAY_RATE = 0.99  # Discount factor
 
 
env = DPendulum()
NX = env.nx  # Number of (discrete) states
NU = env.nu  # Number of (discrete) controls
 
Q = np.zeros([env.nx, env.nu])  # Q-table initialized to 0
 
 
def rendertrial(maxiter=100):
    """Roll-out from random state using greedy policy."""
    s = env.reset()
    for i in range(maxiter):
        a = np.argmax(Q[s, :])
        s, r = env.step(a)
        env.render()
        if r == 1:
            print("Reward!")
            break
 
 
signal.signal(
    signal.SIGTSTP, lambda x, y: rendertrial()
)  # Roll-out when CTRL-Z is pressed
h_rwd = []  # Learning history (for plot).
 
for episode in range(1, NEPISODES):
    x = env.reset()
    rsum = 0.0
    for steps in range(NSTEPS):
        u = np.argmax(
            Q[x, :] + np.random.randn(1, NU) / episode
        )  # Greedy action with noise
        x2, reward = env.step(u)
 
        # Compute reference Q-value at state x respecting HJB
        Qref = reward + DECAY_RATE * np.max(Q[x2, :])
 
        # Update Q-Table to better fit HJB
        Q[x, u] += LEARNING_RATE * (Qref - Q[x, u])
        x = x2
        rsum += reward
        if reward == 1:
            break
 
    h_rwd.append(rsum)
    if not episode % 20:
        print("Episode #%d done with %d sucess" % (episode, sum(h_rwd[-20:])))
 
print("Total rate of success: %.3f" % (sum(h_rwd) / NEPISODES))
rendertrial()
plt.plot(np.cumsum(h_rwd) / range(1, NEPISODES))
plt.show()