# Tag Info

## Hot answers tagged ddpg

5

I will try to give a broad answer, if it's not helpful I'll remove it. When we talk about sampling we are actually talking about the number of interaction required to an agent to learn a good model of the environment. In general I would say that there are two issues related to sample efficiency: 1 the size of the 'action'+'environment states' space 2 the ...

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In order for the algorithm to have stable behavior, the replay buffer should be large enough to contain a wide range of experiences, but it may not always be good to keep everything. The larger the experience replay, the less likely you will sample correlated elements, hence the more stable the training of the NN will be. However, a large experience replay ...

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This is mostly because humans already have information when they start learning the game (priors) that makes them learn it more quickly. We already know to jump on monsters or avoid them or to get gold looking object. When you remove these priors you can see a human is worse at learning these games. (link) Some experiments they tried in the study to ...

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You need to read this 2020 paper by Deepmind: "Revisiting Fundamentals of Experience Replay" Also, to add to the answer by @nbro Assume you implement experience replay as a buffer where the newest memory is stored instead of the oldest. Then, if your buffer contains 100k entries, any memory will remain there for exactly 100k iterations. Such a ...

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The Ornstein Ulhenebck Process is defined as (in the continuous setting) : $$dX_t = -\beta(X_t - \alpha)dt + \sigma dW_t$$ The analogue for this process in the discrete time case which I assume will be applicable in the RL case will be: $$X_{t+1} = X_t -\beta(X_t - \alpha) + \sigma \{W_{t+1}-W_t\}=$$ $$X_{t+1} = (1 -\beta)X_t - \alpha + \sigma \{W_{t+1}-W_t\}... 3 What I want to know is whether I can add expert data to the replay buffer, given that DDPG is an off-policy algorithm? You certainly can, that is indeed one of the advantages of off-policy learning algorithms; they're still "correct", regardless of which policy generated the data that you're learning from (and a human expert providing the ... 2 So does that mean, that the input of the first hidden layer was simply the state and the input of the second hidden layer the output of the first hidden layer concatenated with the actions? Yes. Why would you do that? To have the first layer focus on learning the state value independent of the selected action? How would that help? Neural networks hidden ... 2 I am not an expert in this area. But I believe that the word "Deterministic" is for "Policy" in the "Deterministic Policy" Gradient. It does not mean deterministic environment. Stochastic policy: Probabilistic(random) action choice for a given state. Deterministic policy: one action is chosen for a given state. Deterministic Policy Gradient algorithm ... 2 DDPG is an off-policy algorithm simply because of the objective taking expectation with respect to some other distribution that we are not learning about, i.e. the deterministic policy gradient can be expressed as$$\nabla _{\theta^\mu} J \approx \mathbb{E}_{s_t \sim \rho^\beta} \left[ \nabla _{\theta^\mu} Q(s,a|\theta^Q) | s=s_t, a=\mu(s_t ; \theta ^\mu) \...

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Spinning Up by Open Ai. Be sure to read up Part 3 (Intro to Policy Optimisation) before you move on to : https://spinningup.openai.com/en/latest/algorithms/ddpg.html

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I would recommend doing is allowing your network to output any real number and then clipping the output. For instance, I was working with an agent that had to learn an angle between $[0, 2\pi]$ and $[0, 1]$. If the network outputted e.g. 10 in the first dimension then this would just be clipped to $2\pi$. This way the agent only learns about actions within ...

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Below are some tweaks that helped me accelerate the training of DDPG on a Reacher-like environment: Reducing the neural network size, compared to the original paper. Instead of: 2 hidden layers with 400 and 300 units respectively I used 128 units for both hidden layers. I see in your implementation that you used 256, maybe you could try reducing this. ...

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Here's an incomplete answer, but it may help. Your state is read by the function getExtendedObservation(). This function makes two things : it calls the function getObservation() from this source code, gets a state, and extend this state with three components : relative x,y position and euler angle of block in gripper space But what are the 5 first ...

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First, is it even possible to use DDPG for multi-dimensional continuous action spaces? Yes, DDPG was primarily developed to deal with continuous action space you can find out more here, here and here. I have not found any code examples to learn from and many of the papers I have read are near the limit of my understanding in this area. You can check ...

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I had to change the actions selection function for this and tune some hyper-parameters. Here's what I did to make it converge: Sampled the noise from a standard normal distribution instead of sampling randomly. Changed the polyak constant (tau) from 0.99 to 0.001 (I didn't have an idea of what it should be, so I had just set it randomly in the first try) ...

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This is not quite the loss that is stated in the paper. For standard policy gradient methods the objective is to maximise $v_{\pi_\theta}(s_0)$ -- note that this is analogous to minimising $-v_{\pi_\theta}(s_0)$. This is for a stochastic policy. In DDPG the policy is now assumed to be deterministic. In general, we can write v_\pi(s) = \mathbb{E}_{a\sim\pi}[...

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Actually, I just started inspecting the entries further down in the leaderboard list, and there are in fact more modest architectures, e.g. this one, which uses 3 hidden layers with 8 units each.

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The answer to your first question is because the line 'update the critic by minimising the loss $L = \frac{1}{N} \sum_i \left( y_i - Q(s_i, a_i |\theta^Q)\right)^2$ is implying that you will do this by using a gradient, i.e. you calculate the gradient of the loss wrt the parameters and perform a gradient descent step. For the second question, I am not 100% ...

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(1) You might want look into RND (Random network distillation) which allows usage of a curiosity-based exploration bonus for the agent as an intrinsic reward. You can use the intrinsic reward to complement the sparse extrinsic reward return by the environment. The general idea is to have a randomly initialized fixed target network which encodes the next ...

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In deep reinforcement learning for portfolio optimization, many researchers (Xiong at al. for example) use historical market data for model training. The resulting MDP dynamics is of course completely deterministic (if historical prices are used as states) and there's no real sequentiality involved. Whilst I cannot comment on the specific financial model, I ...

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The specific approaches you mentioned (A3C, DDPG), and usually also other Actor-Critic methods in general, are approaches for the standard single-agent Reinforcement Learning (RL) setting. When trying to apply such algorithms to settings that are actually multi-agent settings, it is indeed common to encounter the problems you describe. They can all be viewed ...

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