README.md

basic_rl (v.0.0.2)

A basic_rl.py provides a simple implementation of SARSA/Q-learning algorithms (specified by -a flag) with epsilon-greedy/softmax policies (specified by -p flag). You can also select the environment other than FrozenLake8x8-v0 using -e flag. It also generates a graphical summary of your simulation.

Type the following command in your console to run the simulation using the default setting.

chmod +x basic_rl.py
./basic_rl.py

If you would like to use the SARSA algorithm with the softmax policy, you can type the following command in your console.

./basic_rl.py -a sarsa -p softmax

To learn more about how to use basic_rl.py, type ./basic_rl.py --help in your console. It will give you the following output.

usage: basic_rl.py [-h] [-a {sarsa,q_learning}] [-p {epsilon_greedy,softmax}]
                   [-e ENVIRONMENT] [-n NEPISODE] [-al ALPHA] [-be BETA]
                   [-bi BETAINC] [-ga GAMMA] [-ep EPSILON] [-ed EPSILONDECAY]
                   [-ms MAXSTEP] [-ka KAPPA]

Use SARSA/Q-learning algorithm with epsilon-greedy/softmax polciy.

optional arguments:
  -h, --help            show this help message and exit
  -a {sarsa,q_learning}, --algorithm {sarsa,q_learning}
                        Type of learning algorithm. (Default: sarsa)
  -p {epsilon_greedy,softmax}, --policy {epsilon_greedy,softmax}
                        Type of policy. (Default: epsilon_greedy)
  -e ENVIRONMENT, --environment ENVIRONMENT
                        Name of the environment provided in the OpenAI Gym.
                        (Default: FrozenLake8x8-v0)
  -n NEPISODE, --nepisode NEPISODE
                        Number of episode. (Default: 20000)
  -al ALPHA, --alpha ALPHA
                        Learning rate. (Default: 0.1)
  -be BETA, --beta BETA
                        Initial value of an inverse temperature. (Default:
                        0.0)
  -bi BETAINC, --betainc BETAINC
                        Linear increase rate of an inverse temperature.
                        (Default: 0.25)
  -ga GAMMA, --gamma GAMMA
                        Discount rate. (Default: 0.99)
  -ep EPSILON, --epsilon EPSILON
                        Fraction of random exploration in the epsilon greedy.
                        (Default: 0.7)
  -ed EPSILONDECAY, --epsilondecay EPSILONDECAY
                        Decay rate of epsilon in the epsilon greedy. (Default:
                        0.995)
  -ms MAXSTEP, --maxstep MAXSTEP
                        Maximum step allowed in a episode. (Default: 100)
  -ka KAPPA, --kappa KAPPA
                        Weight of the most recent terminal reward for
                        computing its running average. (Default: 0.01)

This code is the updated version of the code you found in here. In the current version, a running average of the terminal reward is used to control an exploration rate. This idea of controlling the exploration rate by the terminal reward is suggested by JKCooper2 in here.

basic_rl.py

#!/usr/bin/env python
# basic_rl.py (v0.0.2)

import argparse
parser = argparse.ArgumentParser(description='Use SARSA/Q-learning algorithm with epsilon-greedy/softmax polciy.')
parser.add_argument('-a', '--algorithm', default='sarsa', choices=['sarsa', 'q_learning'],
                    help="Type of learning algorithm. (Default: sarsa)")
parser.add_argument('-p', '--policy', default='epsilon_greedy', choices=['epsilon_greedy', 'softmax'],
                    help="Type of policy. (Default: epsilon_greedy)")
parser.add_argument('-e', '--environment', default='FrozenLake8x8-v0',
                    help="Name of the environment provided in the OpenAI Gym. (Default: FrozenLake8x8-v0)")
parser.add_argument('-n', '--nepisode', default='20000', type=int,
                    help="Number of episode. (Default: 20000)")
parser.add_argument('-al', '--alpha', default='0.1', type=float,
                    help="Learning rate. (Default: 0.1)")
parser.add_argument('-be', '--beta', default='0.0', type=float,
                    help="Initial value of an inverse temperature. (Default: 0.0)")
parser.add_argument('-bi', '--betainc', default='0.25', type=float,
                    help="Linear increase rate of an inverse temperature. (Default: 0.25)")
parser.add_argument('-ga', '--gamma', default='0.99', type=float,
                    help="Discount rate. (Default: 0.99)")
parser.add_argument('-ep', '--epsilon', default='0.7', type=float,
                    help="Fraction of random exploration in the epsilon greedy. (Default: 0.7)")
parser.add_argument('-ed', '--epsilondecay', default='0.995', type=float,
                    help="Decay rate of epsilon in the epsilon greedy. (Default: 0.995)")
parser.add_argument('-ms', '--maxstep', default='100', type=int,
                    help="Maximum step allowed in a episode. (Default: 100)")
parser.add_argument('-ka', '--kappa', default='0.01', type=float,
                    help="Weight of the most recent terminal reward for computing its running average. (Default: 0.01)")
args = parser.parse_args()

import gym
import numpy as np
import os

import matplotlib.pyplot as plt

def softmax(q_value, beta=1.0):
    assert beta >= 0.0
    q_tilde = q_value - np.max(q_value)
    factors = np.exp(beta * q_tilde)
    return factors / np.sum(factors)

def select_a_with_softmax(curr_s, q_value, beta=1.0):
    prob_a = softmax(q_value[curr_s, :], beta=beta)
    cumsum_a = np.cumsum(prob_a)
    return np.where(np.random.rand() < cumsum_a)[0][0]

def select_a_with_epsilon_greedy(curr_s, q_value, epsilon=0.1):
    a = np.argmax(q_value[curr_s, :])
    if np.random.rand() < epsilon:
        a = np.random.randint(q_value.shape[1])
    return a

def main():

    env_type = args.environment
    algorithm_type = args.algorithm
    policy_type = args.policy
    
    # Random seed
    np.random.RandomState(42)

    # Selection of the problem
    env = gym.envs.make(env_type)
    
    # Constraints imposed by the environment
    n_a = env.action_space.n
    n_s = env.observation_space.n

    # Meta parameters for the RL agent
    alpha = args.alpha
    beta = args.beta
    beta_inc = args.betainc
    gamma = args.gamma
    epsilon = args.epsilon
    epsilon_decay = args.epsilondecay

    # Experimental setup
    n_episode = args.nepisode
    print "n_episode ", n_episode
    max_step = args.maxstep

    # Running average of the terminal reward, which is used for controlling an exploration rate
    # (This idea of controlling exploration rate by the terminal reward is suggested by JKCooper2)
    # See https://gym.openai.com/evaluations/eval_xSOlwrBsQDqUW7y6lJOevQ
    kappa = args.kappa
    ave_terminal_r = None
    
    # Initialization of a Q-value table
    q_value = np.zeros([n_s, n_a])

    # Initialization of a list for storing simulation history
    history = []
    
    print "algorithm_type: {}".format(algorithm_type)
    print "policy_type: {}".format(policy_type)

    env.reset()

    np.set_printoptions(precision=3, suppress=True)

    result_dir = 'results-{0}-{1}-{2}'.format(env_type, algorithm_type, policy_type)

    # Start monitoring the simulation for OpenAI Gym
    env.monitor.start(result_dir, force=True)

    for i_episode in xrange(n_episode):

        # Reset a cumulative reward for this episode
        cumu_r = 0

        # Start a new episode and sample the initial state
        curr_s = env.reset()

        # Select the first action in this episode
        if policy_type == 'softmax':
            curr_a = select_a_with_softmax(curr_s, q_value, beta=beta)
        elif policy_type == 'epsilon_greedy':
            curr_a = select_a_with_epsilon_greedy(curr_s, q_value, epsilon=epsilon)
        else:
            raise ValueError("Invalid policy_type: {}".format(policy_type))

        for i_step in xrange(max_step):

            # Get a result of your action from the environment
            next_s, r, done, info = env.step(curr_a)

            # Modification of reward
            # CAUTION: Changing this part of the code in order to get a fast convergence
            # is not a good idea because it is essentially changing the problem setting itself.
            # This part of code was kept not to get fast convergence but to show the 
            # influence of a reward function on the convergence speed for pedagogical reason.
            #if done & (r == 0):
            #    # Punishment for falling into a hall
            #    r = 0.0
            #elif not done:
            #    # Cost per step
            #    r = 0.0

            # Update a cummulative reward
            cumu_r = r + gamma * cumu_r

            # Select an action
            if policy_type == 'softmax':
                next_a = select_a_with_softmax(next_s, q_value, beta=beta)
            elif policy_type == 'epsilon_greedy':
                next_a = select_a_with_epsilon_greedy(next_s, q_value, epsilon=epsilon)
            else:
                raise ValueError("Invalid policy_type: {}".format(policy_type))            

            # Calculation of TD error
            if algorithm_type == 'sarsa':
                delta = r + gamma * q_value[next_s, next_a] - q_value[curr_s, curr_a]
            elif algorithm_type == 'q_learning':
                delta = r + gamma * np.max(q_value[next_s, :]) - q_value[curr_s, curr_a]
            else:
                raise ValueError("Invalid algorithm_type: {}".format(algorithm_type))

            # Update a Q value table
            q_value[curr_s, curr_a] += alpha * delta

            curr_s = next_s
            curr_a = next_a

            if done:

                # Running average of the terminal reward, which is used for controlling an exploration rate
                # (This idea of controlling exploration rate by the terminal reward is suggested by JKCooper2)
                # See https://gym.openai.com/evaluations/eval_xSOlwrBsQDqUW7y6lJOevQ
                kappa = 0.01
                if ave_terminal_r == None:
                    ave_terminal_r = r
                else:
                    ave_terminal_r = kappa * r + (1 - kappa) * ave_terminal_r
                
                if r > ave_terminal_r:
                    # Bias the current policy toward exploitation
                    
                    if policy_type == 'epsilon_greedy':
                        # epsilon is decayed expolentially
                        epsilon = epsilon * epsilon_decay
                    elif policy_type == 'softmax':
                        # beta is increased linearly
                        beta = beta + beta_inc
                        
                if policy_type == 'softmax':
                    print "Episode: {0}\t Steps: {1:>4}\tCumuR: {2:>5.2f}\tTermR: {3}\tAveTermR: {4:.3f}\tBeta: {5:.3f}".format(
                        i_episode, i_step, cumu_r, r, ave_terminal_r, beta)
                    history.append([i_episode, i_step, cumu_r, r, ave_terminal_r, beta])
                elif policy_type == 'epsilon_greedy':
                    print "Episode: {0}\t Steps: {1:>4}\tCumuR: {2:>5.2f}\tTermR: {3}\tAveTermR: {4:.3f}\tEpsilon: {5:.3f}".format(
                        i_episode, i_step, cumu_r, r, ave_terminal_r, epsilon)
                    history.append([i_episode, i_step, cumu_r, r, ave_terminal_r, epsilon])
                else:
                    raise ValueError("Invalid policy_type: {}".format(policy_type))

                break

    # Stop monitoring the simulation for OpenAI Gym
    env.monitor.close()

    history = np.array(history)

    window_size = 100
    def running_average(x, window_size, mode='valid'):
        return np.convolve(x, np.ones(window_size)/window_size, mode=mode)

    fig, ax = plt.subplots(2, 2, figsize=[12, 8])
    # Number of steps
    ax[0, 0].plot(history[:, 0], history[:, 1], '.') 
    ax[0, 0].set_xlabel('Episode')
    ax[0, 0].set_ylabel('Number of steps')
    ax[0, 0].plot(history[window_size-1:, 0], running_average(history[:, 1], window_size))
    # Cumulative reward
    ax[0, 1].plot(history[:, 0], history[:, 2], '.') 
    ax[0, 1].set_xlabel('Episode')
    ax[0, 1].set_ylabel('Cumulative rewards')
    ax[0, 1].plot(history[window_size-1:, 0], running_average(history[:, 2], window_size))
    # Terminal reward
    ax[1, 0].plot(history[:, 0], history[:, 3], '.') 
    ax[1, 0].set_xlabel('Episode')
    ax[1, 0].set_ylabel('Terminal rewards')
    ax[1, 0].plot(history[window_size-1:, 0], running_average(history[:, 3], window_size))
    # Epsilon/Beta
    ax[1, 1].plot(history[:, 0], history[:, 5], '.') 
    ax[1, 1].set_xlabel('Episode')
    if policy_type == 'softmax':
        ax[1, 1].set_ylabel('Beta')
    elif policy_type == 'epsilon_greedy':
        ax[1, 1].set_ylabel('Epsilon')
    fig.savefig('./'+result_dir+'.png')

    print "Q value table:"
    print q_value

    if policy_type == 'softmax':
        print "Action selection probability:"
        print np.array([softmax(q, beta=beta) for q in q_value])
    elif policy_type == 'epsilon_greedy':
        print "Greedy action"
        greedy_action = np.zeros([n_s, n_a])
        greedy_action[np.arange(n_s), np.argmax(q_value, axis=1)] = 1
        #print np.array([zero_vec[np.argmax(q)] = 1 for q in q_value])
        print greedy_action

if __name__ == "__main__":

    main()

An updated version of the code (v0.0.3) can be found in here.

So instead of having a running average of the terminal reward to control an exploration rate, why can't we decay the epsilon whenever we are rewarded '1' and do not decay when we're awarded '0'. Isn't it the same thing?