Questions tagged [reinforcement-learning]

For questions related to learning controlled by external positive reinforcement or negative feedback signal or both, where learning and use of what has been thus far learned occur concurrently.

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60 views

What are the differences between SARSA and Q-learning?

From Sutton and Barto's book Reinforcement Learning (Adaptive Computation and Machine Learning series), are the following definitions: To aid my learning of RL and gain an intuition, I'm focusing on ...
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40 views

Why is the “reward to go” replaced by Q instead of V, when transitioning from PG to actor critic methods?

While transitioning from simple policy gradient to the actor-critic algorithm, most sources begin by replacing the "reward to go" with the state-action value function (see this slide 5). I am not ...
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1answer
49 views

Solution to exercise 3.22 in the RL book by Sutton and Barto

The goal is to find an optimal deterministic policy for this MDP: There are two possible policies: left (L) and right (R). What is the optimal policy, when different discounts are used: A $\gamma =...
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40 views

Generalising performance of Q-learning agent through self-play in a two-player game (MCTS?)

I'm using Q-learning (off-policy TD-control as specified in Sutton's book on pg 131) to train an agent to play connect four. My goal is to create a strong player (superhuman performance?) purely by ...
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1answer
50 views

Soft Actor Critic - Losses are not converging

I'm trying to implement soft actor-critic algorithm for financial data (stock prices) and I have trouble with losses, no matter what combination of HyperParameters I enter, they are not converging, ...
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62 views

How do I know that the DQN has learnt an appropriate Q function?

Is there any sanity check to know whether the Q functions learnt are appropriate in deep Q networks? I know that the Q values for end states should approximate the terminal reward. However, is it ...
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1answer
69 views

Why do my rewards fall using tabular Q-learning as I perform more episodes?

Using the tutorial from: SentDex - Python Programming I added Q Learning to my script that was previously just picking random actions. His script uses the MountainCar Environment so I had to amend it ...
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43 views

Model Based rl and cross entropy method with nonlinear function approximators

Pseudo code for Cross entropy method according to youtube lecture 32:55 Initialize $\mu \in R^{d}, \sigma \in R^{d}$ iteration 1,2,... Collect n samples of $\theta_{i} \sim N(\mu,diag(\sigma))$ ...
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1answer
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Why we don't use importance sampling in tabular Q-Learning?

Why don't we use an importance sampling ratio in Q-Learning, even though Q-Learning is an off-policy method? Importance sampling is used to calculate expectation of a random variable by using data ...
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2answers
144 views

What is the value of a state when there is a certain probability that agent will die after each step?

We assume infinite horizon and discount factor $\gamma = 1$. At each step, after the agent takes an action and gets its reward, there is a probability $\alpha = 0.2$, that agent will die. The assumed ...
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How is per-decision importance sampling derived in Sutton & Barto's book?

In per-decison importance sampling given in Sutton & Barto's book: Eq 5.12 $\rho_{t:T-1}R_{t+k} = \frac{\pi(A_{t}|S_{t})}{b(A_{t}|S_{t})}\frac{\pi(A_{t+1}|S_{t+1})}{b(A_{t+1}|S_{t+1})}\frac{\pi(...
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Why does the n-step return being zero result in high variance in off policy n-step TD?

In the paragraph given between eq 7.12 and 7.13 in Sutton & Barto's book: $G_{t:h} = R_{t+1} + G_{t+1:h} , t < h < T$ where $G_{h:h} = V_{h-1}(S_h)$. (Recall that this return is used at ...
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Problem in understanding equation given for convergence of TD(n) algorithm

Given equation 7.3 of Sutton and Barto's book for convergence of TD(n): $\max_s|\mathbb{E}_\pi[G_{t:t+n}|S_t = s] - v_\pi(s)| \leqslant \gamma^n \max_s|V_{t+n-1}(s) - v_\pi(s)|$ $\textbf{PROBLEM ...
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When we use a neural network to approximate the Q values, is the Q target a single value?

I have two questions When we use our network to approximate our Q values, is the Q target a single value? During backpropagation, when the weights are updated, does it automatically update the Q ...
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62 views

TD-Leaf struggles at learning chess

I am currently working on implementing Giraffe chess algorithm. Following this paper, I designed a neural network similar to the one proposed by the author which I trained using TD-Leaf(lambda). The ...
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27 views

My Double DQN with Experience Replay produces a no-action decision most of the time. Why?

I've written a Double DQN-based stock trading bot using mainly time series stock data. The internal network of the Double DQN is a LSTM which handles the time series data. An Experience Replay buffer ...
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Can Reinforcement Learning be used for UAV waypoint control?

I want to make a drone which can follow static and dynamic waypoints. I am a total beginner in the drone field so I can't figure out that should I use Reinforcement Learning or any other learning ...
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64 views

What is the proof that “reward-to-go” reduces variance of policy gradient?

I am following the OpenAI's spinning up tutorial Part 3: Intro to Policy Optimization. It is mentioned there that the reward-to-go reduces the variance of the policy gradient. While I understand the ...
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2answers
162 views

Why are the value functions sometimes written with capital letters and other times with lower-case letters?

Why are the state-value and action-value functions are sometimes written in small letters and other times in capitals? For instance, why in the Q-learning algorithm (page 131 of Barto and Sutton's ...
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35 views

Why in RL function approximators with recurrent structures can learn planning?

In the paper An Investigation of Model-Free Planning the authors use ConvLSTM to learn a planning function. In particular, for each input x_t at time-step ...
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1answer
110 views

Non-differentiable reward function to update a neural network

In Reinforcement Learning, when reward function is not differentiable, a policy gradient algorithm is used to update the weights of a network. In the paper Neural Architecture Search with ...
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Should the network weights converge when training Deep Q networks?

I have two sets of data, one training and one test set. I use the train set to train the deep q network model variant. I also continuously evaluate the agent Q values obtained on the test set every ...
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1answer
181 views

How do I recognise a bandit problem?

I'm having difficulty understanding the distinction between a bandit problem and a non-bandit problem. An example of the bandit problem is an agent playing $n$ slot machines with the goal of ...
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137 views

How do we express $q_\pi(s,a)$ as a function of $p(s',r|s,a)$ and $v_\pi(s)$?

The task (exercise 3.13 in the RL book by Sutton and Barto) is to express $q_\pi(s,a)$ as a function of $p(s',r|s,a)$ and $v_\pi(s)$. $q_\pi(s,a)$ is the action-value function, that states how good ...
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39 views

If the minimum Q value is decreasing and the maximum Q value increasing, is this a sign that dueling double DQN is diverging?

I'm training a dueling double DQN agent with prioritized replay buffer and notice that the min Q values are decreasing, while the max Q values are increasing. Is this a sign that it is diverging? ...
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1answer
73 views

How does $\mathbb{E}$ suddenly change to $\mathbb{E}_{\pi'}$ in this equation?

In Sutton-Barto's book on page 63 (81 of the pdf): $$\mathbb{E}[R_{t+1} + \gamma v_\pi(S_{t+1}) \mid S_t=s,A_t=\pi'(s)] = \mathbb{E}_{\pi'}[R_{t+1} + \gamma v_\pi(S_{t+1}) \mid S_{t} = s]$$ How does $...
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Should I use exploration strategy in Policy Gradient algorithms?

In policy gradient algorithms the output is a stochastic policy - a probability for each action. I believe that if I follow the policy (sample an action from the policy) I make use of exploration ...
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1answer
132 views

Can I apply DQN or policy gradient algorithms in the contextual bandit setting?

I have a problem which I believe can be described as a contextual bandit. More specifically, in each round, I observe a context from the environment consisting of five continuous features, and, ...
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2answers
93 views

How to convert sequences of images into state in DQN?

I recently read the DQN paper titled: Playing Atari with Deep Reinforcement Learning. My basic and rough understanding of the paper is as follows: You have two neural networks; one stays frozen for a ...
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103 views

Why state-action value function as an expected value of the return and state value function, does not need to follow policy?

I often see, the state-action value function is expressed as: $q_{\pi}(s,a)=\mathbb{E}_{\pi}[R_{t+1}+\gamma G_{t+1} | S_t=s, A_t = a] = \mathbb{E}[R_{t+1}+\gamma v_{\pi}(s') |S_t = s, A_t =a]$ Why ...
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1answer
90 views

How to implement RAM versions of Atari games

I have coded the breakout RAM version, but, unfortunately, its highest reward was 5. I trained it for about 2 hours and never reached a higher score. The code is huge, so I can't paste here, but, in ...
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1answer
65 views

Why does AlphaGo Zero select move based on exponentiated visit count?

From the AlphaGo Zero paper, AlphaGo Zero uses an exponentiated visit count from the tree search. Why use visit count instead of the mean action value $Q(s, a)$?
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How to take actions at each episode and within each step of the episode in deep Q learning?

In deep Q learning, we execute the algorithm for each episode, and for each step within an episode, we take an action and record a reward. I have a situation where my action is 2-tuple $a=(a_1,a_2)$. ...
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1answer
134 views

How to train a reinforcement learning agent from raw pixels?

How would you train a reinforcement learning agent from raw pixels? For example, if you have 3 stacked images to sense motion, then how would you pass them to neural networks to output Q-learning ...
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1answer
47 views

What's the right way of building a deep Q-network?

I'm new to RL and to deep q-learning and I have a simple question about the architecture of the neural network to use in an environment with a continous state space a discrete action space. I tought ...
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1answer
71 views

What is the solution to the exercise 3.11 in the RL book by Sutton and Barto

I'm trying to solve the exercise 3.11 from the second-edition from the Sutton and Barto's book Exercise 3.11 If the current state is $S_t$ , and actions are selected according to a stochastic ...
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34 views

How to choose hyperparameters in double DQN?

I'm looking for some indications about the tuning of hyperparameters in building my double DQN. I have a time series problem (with about 2000 observations and no terminal state, I have to max the ...
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1answer
43 views

When discounted MAB is useful?

Many of multi-armed bandit algorithms are used when the total reward is the sum of all rewards. However, in RL, the discounted reward is mainly used. Why the discounted reward is not prevailing in MAB ...
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2answers
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Why is $G_{t+1}$ is replaced with $v_*(S_{t+1})$ in the Bellman optimality equation?

In equation 3.17 of Sutton and Barto's book: $$q_*(s, a)=\mathbb{E}[R_{t+1} + \gamma v_*(S_{t+1}) \mid S_t = s, A_t = a]$$ $G_{t+1}$ here have been replaced with $v_*(S_{t+1})$, but no reason has ...
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2answers
67 views

Is there any difference between reward and return in reinforcement learning?

I am reading Sutton and Barto's book on reinforcement learning. I thought that reward and return were the same things. However, in Section 5.6 of the book, 3rd line, first paragraph, it is written: ...
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1answer
67 views

How is $\Delta$ updated in true online TD($\lambda$)?

In the RL textbook by Sutton & Barto section 7.4, the author talked about the "True online TD($\lambda$)". The figure (7.10 in the book) below shows the algorithm. At the end of each step, $V_{...
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2answers
63 views

Are there any good tutorials about training RL agent from raw pixels using PyTorch?

Is there any good tutorials about training reinforcement learning agent from raw pixels using PyTorch? I don't understand the official PyTorch tutorial. I want to train the agent on the atari ...
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26 views

Is there any advantage to using a non-diagonal covariance matrix for a policy distribution?

For reinforcement learning implementations with a gym.spaces.Box action space, which is the product of $k$ real closed intervals, it is common (actually more like ...
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1answer
47 views

What is correct update when the some indexes are not available?

To update the Q table Q-learning takes the arg max of the Q values - the state, value mappings. For example, in tic tac toe the state XOX OXO -X- contains two ...
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How can the target rely on untrained parameters?

I'm trying to understand DQN. I understand where the loss function comes from. I'm just unsure about why the target function works in practice. Given the loss function $$ L_i(\theta_i) = [(y_i - Q(s,a;...
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1answer
63 views

What is the difference between reinforcement learning and evolutionary algorithms?

What is the difference between reinforcement learning (RL) and evolutionary algorithms (EA)? For some problems, you could presumably co-evolve two "species" populations using evolutionary algorithms ...
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0answers
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Are the final states not being updated in this $n$-step Q-Learning algorithm?

I am reading this paper and in algorithm 3 they describe an $n$-step Q-Learning algorithm. Below is the pseudo-code. From this pseudo-code, it looks as though the final tuples that they would ...
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1answer
44 views

What is meant by the rank of the scoring function here?

I've been reading this paper on Knowledge Graph Reasoning for Explainable Recommendation lately, and I don't understand a particular section: Specifically, the scoring function $f((r,e)|u)$ maps any ...
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1answer
65 views

Is there any programming practice website for beginners in Reinforcement Learning [closed]

I am doing an online course on Reinforcement Learning from university of Alberta. It focus too much on theory. I am engineering and I am interested towards applying RL to my applications directly. ...
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49 views

Calculating the advantage 'gain' of actions in model-free reinforcement learning

I have a simple question about model-free reinforcement. In a model I'm writing about, I want to know the value 'gain' we'd get for executing an action, relative to the current state. That is, what ...

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