In recent years, reinforcement learning has been combined with deep neural networks, giving rise to game agents with super-human performance (for example for Go, chess, or 1v1 Dota2, capable of being trained solely by self-play), datacenter cooling algorithms being 50% more efficient than trained human operators, or improved machine translation. The goal of the course is to introduce reinforcement learning employing deep neural networks, focusing both on the theory and on practical implementations.
Python programming skills and TensorFlow skills (or any other deep learning framework) are required, to the extent of the NPFL114 course. No previous knowledge of reinforcement learning is necessary.
SIS code: NPFL122
Semester: winter
E-credits: 6
Examination: 2/2 C+Ex
Guarantor: Milan Straka
1. Introduction to Reinforcement Learning Slides PDF Slides multiarmed_bandits
2. Markov Decision Process, Optimal Solutions, Monte Carlo Methods Slides PDF Slides policy_iteration monte_carlo
3. Temporal Difference Methods, Off-Policy Methods Slides PDF Slides q_learning importance_sampling lunar_lander
4. N-step Methods, Function Approximation Slides PDF Slides q_learning_tiles
5. Function Approximation, Deep Q Network Slides PDF Slides q_network
6. Rainbow Slides PDF Slides car_racing reinforce
7. Policy Gradient Methods Slides PDF Slides reinforce_with_baseline cart_pole_pixels
8. Advantage Actor-Critic, Continuous Action Space Slides PDF Slides paac paac_continuous
9. Deterministic Policy Gradient, Advanced RL Algorithms Slides PDF Slides ddpg walker
10. TD3, Monte Carlo Tree Search Slides PDF Slides walker_hardcore az_quiz az_quiz_randomized
11. V-trace, PopArt Normalization, Partially Observable MDPs Slides PDF Slides vtrace memory_game
To pass the practicals, you need to complete at least 80% of compulsory home assignments. Several additional voluntary assignments will be available, and up to 40 points from these will be transfered to the exam.
To pass the exam, you need to obtain at least 60, 75 and 90 out of 100 points for the written exam (plus up to 40 points from the practicals), to obtain grades 3, 2 and 1, respectively.
The lecture content, including references to study materials.
The main study material is the Reinforcement Learning: An Introduction; second edition by Richard S. Sutton and Andrew G. Barto (reffered to as RLB). It is available online and also as a hardcopy since October 15, 2018.
References to study materials cover all theory required at the exam, and sometimes even more – the references in italics cover topics not required for the exam.
Oct 08 Slides PDF Slides multiarmed_bandits
Oct 15 Slides PDF Slides policy_iteration monte_carlo
Oct 22 Slides PDF Slides q_learning importance_sampling lunar_lander
Nov 05 Slides PDF Slides q_learning_tiles
Nov 12 Slides PDF Slides q_network
Nov 19 Slides PDF Slides car_racing reinforce
Nov 26 Slides PDF Slides reinforce_with_baseline cart_pole_pixels
Dec 03 Slides PDF Slides paac paac_continuous
Dec 10 Slides PDF Slides ddpg walker
Dec 17 Slides PDF Slides walker_hardcore az_quiz az_quiz_randomized
Jan 07 Slides PDF Slides vtrace memory_game
You should submit the assignments in the ReCodEx Code Examiner, where they will be either automatically or manually evaluated (depending on the assignment). The evaluation is performed using Python 3.6, TensorFlow 1.11.0, NumPy 1.15.2 and OpenAI Gym 0.9.5. For those using PyTorch, CPU version 1.0.0 is available.
You can install TensorFlow and Gym either to user packages using
pip3 install --user tensorflow==1.11.0 gym==0.9.5 scipy box2d-py atari-py
(with the last three backages being optinal dependencies of gym
),
or create a virtual environment using python3 -m venv VENV_DIR
and then installing
the packages inside it by running
VENV_DIR/bin/pip3 install tensorflow==1.11.0 gym==0.9.5 scipy box2d-py atari-py
.
On Windows, you can use third-party precompiled versions of
box2d-py
and atari-py.
Note that when your CPU does not support AVX, you need to install TensorFlow 1.5.
Even if ReCodEx allows submitting data files
beside Python sources, the data files are not available during evaluation.
Therefore, in order to submit models, you need to embed them in Python sources.
You can use the embed.py
script,
which compressed and embeds given files and directories into a Python module
providing an extract()
method.
Working in teams of size 2 (or at most 3) is encouraged. All members of the team must submit in ReCodEx individually, but can have exactly the same sources/models/results. However, each such solution must explicitly list all members of the team to allow plagiarism detection using this template.
Deadline: Oct 21, 23:59 compulsory
Perform a parameter study of various approaches to solving multiarmed bandits. For every hyperparameter choice, perform 1000 episodes, each consisting of 1000 trials, and report averaged return (a single number).
Start with the multiarmed_bandits.py
template, which defines MultiArmedBandits
environment. We use API based on
OpenAI Gym Environment
class, notably the following
two methods:
reset() → new_state
: starts a new episodestep(action) → new_state, reward, done, info
: perform the chosen action
in the environment, returning the new state, obtained reward, a boolean
flag indicating an end of episode, and additional environment-specific
information
Of course, the states are not used by the multiarmed bandits (None
is
returned).Your goal is to implement the following modes of calculation. For each mode evaluate the performance given specified hyperparameters and plot the results for all modes together in a single graph.
greedy
: perform $ε$-greedy search with parameter epsilon
, computing the
value function using averaging. Plot results for
$ε ∈ \{1/64, 1/32, 1/16, 1/8, 1/4\}$.greedy
and alpha
$≠0$: perform $ε$-greedy search with parameter epsilon
and
initial function estimate of 0, using fixed learning rate alpha
. Plot
results for $α=0.15$ and $ε ∈ \{1/64, 1/32, 1/16, 1/8, 1/4\}$greedy
, alpha
$≠0$ and initial
$≠0$: perform $ε$-greedy search with
parameter epsilon
, given initial
value as starting value function and
fixed learning rate alpha
. Plot results for initial
$=1$, $α=0.15$ and
$ε ∈ \{1/128, 1/64, 1/32, 1/16\}$.ucb
: perform UCB search with confidence level c
and computing the value
function using averaging. Plot results for $c ∈ \{1/4, 1/2, 1, 2, 4\}$.gradient
: choose actions according to softmax distribution, updating the
parameters using SGD to maximize expected reward. Plot results for
$α ∈ \{1/16, 1/8, 1/4, 1/2\}$.This task will be evaluated manually and you should submit the Python source and the generated graph.
Deadline: Oct 28, 23:59 compulsory
Consider the following gridworld:
Start with policy_iteration.py, which implements the gridworld mechanics, by providing the following methods:
GridWorld.states
: return number of states (11
)GridWorld.actions
: return lists with labels of the actions (["↑", "→", "↓", "←"]
)GridWorld.step(state, action)
: return possible outcomes of performing the
action
in a given state
, as a list of triples containing
probability
: probability of the outcomereward
: reward of the outcomenew_state
: new state of the outcomeImplement policy iteration algorithm, with --steps
steps of policy
evaluation/policy improvement. During policy evaluation, use the current value
function and perform --iterations
applications of the Bellman equation.
Perform the policy evaluation synchronously (i.e., do not overwrite the current
value function when computing its improvement). Assume the initial policy is
“go North” and initial value function is zero.
After given number of steps and iterations, print the resulting value function and resulting policy. For example, the output after 4 steps and 4 iterations should be:
9.15→ 10.30→ 11.32→ 12.33↑
8.12↑ 3.35← 2.58←
6.95↑ 5.90← 4.66← -4.93↓
Deadline: Oct 28, 23:59 compulsory
Solve the CartPole-v1 environment environment from the OpenAI Gym using the Monte Carlo reinforcement learning algorithm.
Use the supplied cart_pole_evaluator.py module (depending on gym_evaluator.py) to interact with the discretized environment. The environment has the following methods and properties:
states
: number of states of the environmentactions
: number of actions of the environmentepisode
: number of the current episode (zero-based)reset(start_evaluate=False) → new_state
: starts a new episodestep(action) → new_state, reward, done, info
: perform the chosen action
in the environment, returning the new state, obtained reward, a boolean
flag indicating an end of episode, and additional environment-specific
informationrender()
: render current environment stateOnce you finish training (which you indicate by passing start_evaluate=True
to reset
), your goal is to reach an average return of 490 during 100
evaluation episodes. Note that the environment prints your 100-episode
average return each 10 episodes even during training.
You can start with the monte_carlo.py template, which parses several useful parameters, creates the environment and illustrates the overall usage.
During evaluation in ReCodEx, three different random seeds will be employed, and you need to reach the required return on all of them. Time limit for each test is 5 minutes.
Deadline: Nov 04, 23:59 compulsory
Solve the MountainCar-v0 environment environment from the OpenAI Gym using the Q-learning reinforcement learning algorithm. Note that this task does not require TensorFlow.
Use the supplied mountain_car_evaluator.py
module (depending on gym_evaluator.py)
to interact with the discretized environment. The environment
methods and properties are described in the monte_carlo
assignment.
Your goal is to reach an average reward of -150 during 100 evaluation episodes.
You can start with the q_learning.py template, which parses several useful parameters, creates the environment and illustrates the overall usage. Note that setting hyperparameters of Q-learning is a bit tricky – I usualy start with a larger value of $ε$ (like 0.2 or even 0.5) an then gradually decrease it to almost zero.
During evaluation in ReCodEx, three different random seeds will be employed, and you need to reach the required return on all of them. The time limit for each test is 5 minutes.
Deadline: Nov 04, 23:59 compulsory
Using the FrozenLake-v0 environment environment, implement Monte Carlo weighted importance sampling to estimate state value function $V$ of target policy, which uniformly chooses either action 1 (down) or action 2 (right), utilizing behaviour policy, which uniformly chooses among all four actions.
Start with the importance_sampling.py template, which creates the environment and generates episodes according to behaviour policy.
For $1000$ episodes, the output of your program should be the following:
0.00 0.00 0.00 0.00
0.00 0.00 0.00 0.00
0.00 0.00 0.21 0.00
0.00 0.00 0.45 0.00
Deadline: Nov 11, 23:59 compulsory & 7 bonus
Solve the LunarLander-v2 environment environment from the OpenAI Gym. Note that this task does not require TensorFlow.
Use the supplied lunar_lander_evaluator.py
module (depending on gym_evaluator.py
to interact with the discretized environment. The environment
methods and properties are described in the monte_carlo
assignment,
but include one additional method:
expert_trajectory() → initial_state, trajectory
This method generates
one expert trajectory and returns a pair of initial_state
and trajectory
,
where trajectory
is a list of the tripples (action, reward, next_state).
You can use this method only during training, not during evaluation.To pass the task, you need to reach an average return of 0 during 100 evaluation episodes. During evaluation in ReCodEx, three different random seeds will be employed, and you need to reach the required return on all of them. Time limit for each test is 5 minutes.
The task is additionally a competition and at most 7 points will be awarded according to relative ordering of your solution performances.
You can start with the lunar_lander.py template, which parses several useful parameters, creates the environment and illustrates the overall usage.
Deadline: Nov 18, 23:59 compulsory
Improve the q_learning
task performance on the
MountainCar-v0 environment
environment using linear function approximation with tile coding.
Your goal is to reach an average reward of -110 during 100 evaluation episodes.
Use the updated mountain_car_evaluator.py
module (depending on updated gym_evaluator.py)
to interact with the discretized environment. The environment
methods and properties are described in the monte_carlo
assignment, with the
following changes:
The env.weights
method return the number of weights of the linear function
approximation.
The state
returned by the env.step
method is a list containing weight
indices of the current state (i.e., the feature vector of the state consists
of zeros and ones, and only the indices of the ones are returned). The
(action-)value function for a state is therefore approximated as a sum of the
weights whose indices are returned by env.step
.
The default number of tiles in tile encoding (i.e., the size of the list with
weight indices) is args.tiles=8
, but you can use any number you want (but
the assignment is solvable with 8).
You can start with the q_learning_tiles.py template, which parses several useful parameters, creates the environment and illustrates the overall usage. Implementing Q-learning is enough to pass the assignment, even if both N-step Sarsa and Tree Backup converge a little faster.
During evaluation in ReCodEx, three different random seeds will be employed, and you need to reach the required return on all of them. The time limit for each test is 5 minutes.
Deadline: Nov 25, 23:59 compulsory
Solve the CartPole-v1 environment environment from the OpenAI Gym using Q-learning with neural network as a function approximation.
The supplied cart_pole_evaluator.py
module (depending on gym_evaluator.py)
can also create a continuous environment using environment(discrete=False)
.
The continuous environment is very similar to the discrete environment, except
that the states are vectors of real-valued observations with shape environment.state_shape
.
Use Q-learning with neural network as a function approximation, which for a given states returns state-action values for all actions. You can use any network architecture, but two hidden layers of 20 ReLU units are a good start.
Your goal is to reach an average return of 400 during 100 evaluation episodes.
You can start with the q_network.py template, which provides a simple network implementation in TensorFlow.
During evaluation in ReCodEx, two different random seeds will be employed, and you need to reach the required return on all of them. Time limit for each test is 10 minutes (so you can train in ReCodEx, but you can also pretrain your network if you like).
Deadline: Dec 2, 23:59 10 bonus only
Nov 27: The evaluator has been returning a reference to the same numpy array with the state, which could have caused problems if you did not create a copy (when stacking images or resizing it). It has now been fixed.
In this bonus-only exercise to play with Deep Q Network and its variants, try solving the CarRacing-v0 environment environment from the OpenAI Gym.
Use the supplied car_racing_evaluator.py module (depending on gym_evaluator.py to interact with the environment. The environment is continuous and states are RGB images of size $96×96×3$, but you can downsample them even more. The actions are also continuous and consist of an array with the following three elements:
steer
in range [-1, 1]gas
in range [0, 1]brake
in range [0, 1]Internally you should generate discrete actions and convert them to the required
representation before the step
call. Good initial action space is to use
9 actions – a Cartesian product of 3 steering actions (left/right/none) and
3 driving actions (gas/brake/none).
The environment supports frame skipping without
rendering the skipped frames – the second argument to env.step
determines
how many time is the given action repeated.
The task is a competition and at most 10 points will be awarded according to relative ordering of your solution performances. In ReCodEx, your solution is evaluated on 15 different tracks with a total time limit of 15 minutes. If your average return is at least 100, ReCodEx shows the solution as correct.
The car_racing.py template parses several useful parameters and creates the environment. Note that the car_racing_evaluator.py can be executed directly and in that case you can drive the car using arrows.
Deadline: Dec 02, 23:59 compulsory
Solve the CartPole-v1 environment environment from the OpenAI Gym using the REINFORCE algorithm.
The supplied cart_pole_evaluator.py
module (depending on gym_evaluator.py)
can create a continuous environment using environment(discrete=False)
.
The continuous environment is very similar to the discrete environment, except
that the states are vectors of real-valued observations with shape environment.state_shape
.
Your goal is to reach an average return of 490 during 100 evaluation episodes.
You can start with the reinforce.py template, which provides a simple network implementation in TensorFlow.
During evaluation in ReCodEx, two different random seeds will be employed, and you need to reach the required return on all of them. Time limit for each test is 5 minutes.
Deadline: Dec 09, 23:59 compulsory
This is a continuation of reinforce
assignment.
Using the reinforce_with_baseline.py template, solve the CartPole-v1 environment environment using the REINFORCE with baseline algorithm.
Using a baseline lowers the variance of the value function gradient estimator, which allows faster training and decreases sensitivity to hyperparameter values. To reflect this effect in ReCodEx, note that the evaluation phase will automatically start after 200 episodes. Using only 200 episodes for training in this setting is probably too little for the REINFORCE algorithm, but suffices for the variant with a baseline.
Your goal is to reach an average return of 490 during 100 evaluation episodes.
During evaluation in ReCodEx, two different random seeds will be employed, and you need to reach the required return on all of them. Time limit for each test is 5 minutes.
Deadline: Dec 09, 23:59 compulsory & 7 bonus
The supplied cart_pole_pixels_evaluator.py
module (depending on gym_evaluator.py)
generates a pixel representation of the CartPole
environment
as an $80×80$ image with three channels, with each channel representing one time step
(i.e., the current observation and the two previous ones).
To pass the compulsory part of the assignment, you need to reach an average return of 50 during 100 evaluation episodes. During evaluation in ReCodEx, two different random seeds will be employed, and you need to reach the required return on all of them. Time limit for each test is 10 minutes.
The task is additionally a competition and at most 7 points will be awarded according to relative ordering of your solution performances.
The cart_pole_pixels.py
template parses several parameters, creates the environment
and shows how to save and load neural networks in TensorFlow.
To upload the trained model to ReCodEx, you need to embed the
trained model files using embed.py,
submit the resulting embedded_data.py
along your solution, and
in your solution you need to import embedded_data
and then
embedded_data.extract()
(the template does this for you).
Deadline: Dec 16, 23:59 compulsory
Using the paac.py template, solve the CartPole-v1 environment environment using parallel actor-critic algorithm.
The gym_environment
now provides the following two methods:
parallel_init(num_workers) → initial_states
, which initializes the given
number of parallel workers and returns their environment initial states.
This method can be called at most once.parallel_step(actions) → List[next_state, reward, done, info]
, which
performs given action in respective environment, and return the usual
information with one exception: If done=True
, then next_state
is
already a new state of newly started episode.Your goal is to reach an average return of 450 during 100 evaluation episodes.
During evaluation in ReCodEx, two different random seeds will be employed, and you need to reach the required return on all of them. Time limit for each test is 10 minutes.
Deadline: Dec 16, 23:59 compulsory
Using the paac_continuous.py template, solve the MountainCarContinuous-v0 environment environment using parallel actor-critic algorithm with continuous actions.
The gym_environment
now provides two additional methods:
action_shape
: returns required shape of continuous action. You can
assume the actions are always an one-dimensional vector.action_ranges
: returns a pair of vectors low
, high
. These denote
valid ranges for the actions, so low[i]
$≤$action[i]
$≤$high[i]
.Your goal is to reach an average return of 90 during 100 evaluation episodes.
During evaluation in ReCodEx, two different random seeds will be employed, and you need to reach the required return on all of them. Time limit for each test is 10 minutes.
Deadline: Jan 06, 23:59 compulsory
Using the ddpg.py template, solve the Pendulum-v0 environment environment using deep deterministic policy gradient algorithm.
To create the evaluator, use
gym_evaluator.py.GymEvaluator("Pendulum-v0")
.
The environment is continuous, states and actions are described at
OpenAI Gym Wiki.
Your goal is to reach an average return of -200 during 100 evaluation episodes.
During evaluation in ReCodEx, two different random seeds will be employed, and you need to reach the required return on all of them. Time limit for each test is 10 minutes.
Deadline: Jan 06, 23:59 10 bonus only
In this bonus-only exercise exploring continuous robot control, try solving the BipedalWalker-v2 environment environment from the OpenAI Gym.
To create the evaluator, use
gym_evaluator.py.GymEvaluator("BipedalWalker-v2")
.
The environment is continuous, states and actions are described at
OpenAI Gym Wiki.
The task is a competition and at most 10 points will be awarded according to relative ordering of your solution performances. In ReCodEx, your solution will be evaluated on 100 different tracks with a total time limit of 10 minutes. If your average return is at least 0, ReCodEx shows the solution as correct.
You can start with the ddpg.py
template, only set args.env
to BipedalWalker-v2
.
Deadline: Jan 06, 23:59 5 bonus only
As an extesnion of the walker
assignment, try solving the
BipedalWalkerHardcore-v2 environment
environment from the OpenAI Gym.
The task is a competition and at most 5 points will be awarded according to relative ordering of your solution performances. In ReCodEx, your solution will be evaluated on 100 different tracks with a total time limit of 10 minutes. If your average return is at least 0, ReCodEx shows the solution as correct.
You can start with the ddpg.py
template, only set args.env
to BipedalWalkerHardcore-v2
.
Deadline: Jan 13, 23:59 10 bonus only
In this bonus-only exercise, use Monte Carlo Tree Search to learn an agent for a simplified version of AZ-kvíz. In our version, the agent does not have to answer questions and we assume that all answers are correct.
The game itself is implemented in the
az_quiz.py
module, using randomized=False
constructor argument.
The evaluation in ReCodEx should be implemented by importing a module
az_quiz_evaluator_recodex
and calling its evaluate
function. The argument
this functions is an object providing a method play
which given an AZ-kvíz
instance returns the chosen move. The illustration of the interface is in the
az_quiz_evaluator_recodex.py
module.
Your solution in ReCodEx is automatically evaluated only against a random player az_quiz_player_random.py and a very simple heuristic az_quiz_player_simple_heuristic.py, playing against each of them 10 games as a starting player and 10 games as a non-starting player. The time limit for the games is 10 minutes and you should see win rate directly in ReCodEx. The final evaluation will be performed after the deadline by a round-robin tournament, utilizing your latest submission with non-zero win rate.
For inspiration, use the official pseudocode for AlphaZero.
Deadline: Jan 13, 23:59 5 bonus only
Extend the az_quiz
assignment to handle the possibility of wrong
answers. Therefore, when choosing a field, the agent might answer
incorrectly.
To instantiate this randomized game variant, pass randomized=True
to the AZQuiz
class of az_quiz.py.
The Monte Carlo Tree Search has to be slightly modified to handle stochastic
MDP. The information about distribution of possible next states is provided
by the AZQuiz.all_moves
method, which returns a list of (probability, az_quiz_instance)
next states (in our environment, there are always two
possible next states).
The evaluation in ReCodEx should be implemented by importing a module
az_quiz_evaluator_recodex
and calling its evaluate
function. The argument
this functions is an object providing a method play
which given an AZ-kvíz
instance returns the chosen move. The illustration of the interface is in the
az_quiz_evaluator_recodex.py
module.
Your solution in ReCodEx is automatically evaluated only against a random player az_quiz_player_random.py and a very simple heuristic az_quiz_player_simple_heuristic.py, playing against each of them 10 games as a starting player and 10 games as a non-starting player. The time limit for the games is 10 minutes and you should see win rate directly in ReCodEx. The final evaluation will be performed after the deadline by a round-robin tournament, utilizing your latest submission with non-zero win rate.
For inspiration, use the official pseudocode for AlphaZero.
Deadline: Jan 20, 23:59 compulsory
Using the vtrace.py template, implement the V-trace algorithm.
The template uses the CartPole-v1
environment and a replay buffer to more
thoroughly test the off-policy capability of the V-trace algorithm.
However, the evaluation in ReCodEx will be performed by calling only the
vtrace
method and comparing its results to a reference implementation.
Several values of hyperparameters will be used, each test has a time limit
of 1 minute, and all tests must pass.
Deadline: Feb 17, 23:59 5 bonus only
In this bonus-only exercise we explore a partially observable environment. Consider a one-player variant of a memory game (pexeso), where a player repeatedly flip cards. If the player flips two cards with the same symbol in succession, the cards are removed and the player recieves a reward of +2. Otherwise the player recieves a reward of -1. An episode ends when all cards are removed. For a given even $N$, there are $N$ actions – the card indices, and $N/2$ observations, which encode card symbol. Every episode can be ended using at most $3N/2$ actions. The environment is provided by the memory_game_evaluator.py module.
Your goal is to solve the environment using an agent utilizing a LSTM cell. The reinforce algorithm with baseline seems an appropriate choice.
ReCodEx evaluates your solution on environments with 4, 6, 8 and 16 cards
(utilizing the --cards
argument). For each card number, 1000 episodes are
simulated and your solution gets 1 point (2 points for 16 cards) if the average
return is positive.
A template memory_game.py
is available. Depending on memory_cells
argument, it employs either a vanilla
LSTM or LSTM with external memory. Note that I was able to train it only for 4, 6,
and 8 cards.
Lecture 1: Introduction to Reinforcement Learning
Lecture 2: Markov Decision Process, Optimal Solutions, Monte Carlo Methods
Lecture 3: Temporal Difference Methods, Off-Policy Methods
Lecture 4: N-step Methods, Function Approximation
Lecture 5: Function Approximation, Deep Q Network
Lecture 6: Rainbow
Lecture 7: Policy Gradient Methods
Lecture 8: Advantage Actor-Critic, Continuous Action Space
Lecture 9: Deterministic Policy Gradient, Advanced RL Algorithms
Lecture 10: TD3, Monte Carlo Tree Search
Lecture 11: V-trace, PopArt Normalization, Partially Observable MDPs