Questions tagged [model-free-methods]

For questions about model-free reinforcement learning methods (or algorithms). An example of a model-free algorithm is Q-learning, which does not use the transition function (i.e. the model) of the environment (or Markov decision process).

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Why is even q estimation reduced but the agent cannot predict correctly after training? (offline q learning)

I am going to implement Algorithm 1 in this paper. When I train the agent, it was gradually reduced the q estimate and, after training agent cannot predict correctly. What is the reason for that?
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59 views

Reinforcement learning - confusion between model based and model free

I have have an environment with two models. Model of the environment is stochastic. Given the price it returns the time when the next purchase will be made and how many items will be bought. Both of ...
0 votes
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How to evaluate the performance of off-line & model-free reinforcement leaning?

I'm currently studying on off-line reinforcement learning (RL) and trying to utilize it for medical data. Because it seemed hard to develop well-performing environment model, I decided to adopt model-...
2 votes
1 answer
45 views

How to prove importance sampling ratio is uncorrelated with action-value (or state-value) estimate?

In Sutton & Barto (2nd edition), the following is mentioned on page 150 (p. 172 of the pdf), section 7.4: the importance sampling ratio has expected value one (Section 5.9) and is uncorrelated ...
0 votes
1 answer
108 views

Why don't we bootstrap terminal state in n-step temporal difference prediction update equation?

In the algorithm below, when $\tau + n \geq T$, shouldn't the algorithm bootstrap with the value of the next state? For instance, when $T=5, \tau=3, \& \; n=2$, we don't bootstrap the sample ...
0 votes
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Why does one-step TD strengthen only the last action of the sequence of actions that led to the high reward, while n-step TD the last n actions?

In the caption of figure 7.4 (p. 147) of Sutton & Barto's book (2nd edition), it's written The one-step method strengthens only the last action of the sequence of actions that led to the high ...
0 votes
0 answers
56 views

How does n-step Temporal Difference remove the notion of time-step?

How does n-step TD removes the notion of time-step as referenced in Sutton and Barto (2nd edition, Page 163) below? Another way of looking at the benefits of n-step methods is that they free you from ...
1 vote
1 answer
371 views

In deep reinforcement learning, what is this model with state as input and value as output?

I was looking at this implementation for creating an agent for playing Tetris using DeepRL. This model uses "a state based on the statistics of the board after a potential action. All predictions ...
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2 votes
1 answer
64 views

If we can model the environment, wouldn't be meaningless to use a model-free algorithm?

I am trying to understand the concept of model-free and model-based approaches. As far as I understand, having a model of the environment does not mean that an RL agent has to be model-based. It is ...
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2 votes
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93 views

What kind of reinforcement learning method does AlphaGo Deepmind use to beat the best human Go player?

In reinforcement learning, there are model-based versus model-free methods. Within model-based ones, there are policy-based and value-based methods. AlphaGo Deepmind RL model has beaten the best Go ...
1 vote
1 answer
326 views

Why does Monte Carlo policy evaluation relies on action-value function rather than state-value function?

Here is David Silver's lecture on that. Look at 9:30 to 10:30. He says that, since it is model-free learning, the environment's dynamics are unknown, so the action-value function $Q$ is used. But ...
4 votes
1 answer
321 views

Why are state-values alone not sufficient in determining a policy (without a model)?

"If a model is not available, then it is particularly useful to estimate action values (the values of state-action pairs) rather than state values. With a model, state values alone are sufficient ...
2 votes
1 answer
105 views

Into which subcategories can reinforcement learning be divided?

In the course of a scientific work, I will discuss the different types of reinforcement learning. However, I have difficulties to find these different types. So, into which subcategories can ...
5 votes
2 answers
435 views

How can the policy iteration algorithm be model-free if it uses the transition probabilities?

I'm actually trying to understand the policy iteration in the context of RL. I read an article presenting it and, at some point, a pseudo-code of the algorithm is given : What I can't understand is ...
4 votes
1 answer
436 views

How does policy evaluation work for continuous state space model-free approaches?

How does policy evaluation work for continuous state space model-free approaches? Theoretically, a model-based approach for the discrete state and action space can be computed via dynamic programming ...
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4 votes
1 answer
301 views

Is the minimax algorithm model-based?

Trying to get my head around model-free and model-based algorithms in RL. In my research, I've seen the search trees created via the minimax algorithm. I presume these trees can only be created with a ...
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3 votes
1 answer
1k views

Are model-free and off-policy algorithms the same?

In respect of RL, is model-free and off-policy the same thing, just different terminology? If not, what are the differences? I've read that the policy can be thought of as 'the brain', or decision ...
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4 votes
1 answer
1k views

Why are model-based methods more sample efficient than model-free methods?

Why do model-based methods use fewer samples than model-free methods? Here, I'm specifically referring to model-based methods in which we have to learn a policy and model. I can only think of two ...
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2 votes
1 answer
730 views

What is the relation between Monte Carlo and model-free algorithms?

Monte Carlo (MC) methods are methods that use some form of randomness or sampling. For example, we can use an MC method to approximate the area of a circle inside a square: we generate random 2D ...
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1 vote
2 answers
1k views

How can we estimate the transition model and reward function?

In reinforcement learning (RL), there are model-based and model-free algorithms. In short, model-based algorithms use a transition model $p(s' \mid s, a)$ and the reward function $r(s, a)$, even ...
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4 votes
1 answer
163 views

How do temporal-difference and Monte Carlo methods work, if they do not have access to model?

In value iteration, we have a model of the environment's dynamics, i.e $p(s', r \mid s, a)$, which we use to update an estimate of the value function. In the case of temporal-difference and Monte ...
77 votes
6 answers
84k views

What's the difference between model-free and model-based reinforcement learning?

What's the difference between model-free and model-based reinforcement learning? It seems to me that any model-free learner, learning through trial and error, could be reframed as model-based. In ...