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hf_public_repos/deep-rl-class/units/en | hf_public_repos/deep-rl-class/units/en/unit5/curiosity.mdx | # (Optional) What is Curiosity in Deep Reinforcement Learning?
This is an (optional) introduction to Curiosity. If you want to learn more, you can read two additional articles where we dive into the mathematical details:
- [Curiosity-Driven Learning through Next State Prediction](https://medium.com/data-from-the-trenches/curiosity-driven-learning-through-next-state-prediction-f7f4e2f592fa)
- [Random Network Distillation: a new take on Curiosity-Driven Learning](https://medium.com/data-from-the-trenches/curiosity-driven-learning-through-random-network-distillation-488ffd8e5938)
## Two Major Problems in Modern RL
To understand what Curiosity is, we first need to understand the two major problems with RL:
First, the *sparse rewards problem:* that is, **most rewards do not contain information, and hence are set to zero**.
Remember that RL is based on the *reward hypothesis*, which is the idea that each goal can be described as the maximization of the rewards. Therefore, rewards act as feedback for RL agents; **if they don’t receive any, their knowledge of which action is appropriate (or not) cannot change**.
<figure>
<img src="https://huggingface.co/datasets/huggingface-deep-rl-course/course-images/resolve/main/en/unit5/curiosity1.png" alt="Curiosity"/>
<figcaption>Source: Thanks to the reward, our agent knows that this action at that state was good</figcaption>
</figure>
For instance, in [Vizdoom](https://vizdoom.cs.put.edu.pl/), a set of environments based on the game Doom “DoomMyWayHome,” your agent is only rewarded **if it finds the vest**.
However, the vest is far away from your starting point, so most of your rewards will be zero. Therefore, if our agent does not receive useful feedback (dense rewards), it will take much longer to learn an optimal policy, and **it can spend time turning around without finding the goal**.
<img src="https://huggingface.co/datasets/huggingface-deep-rl-course/course-images/resolve/main/en/unit5/curiosity2.png" alt="Curiosity"/>
The second big problem is that **the extrinsic reward function is handmade; in each environment, a human has to implement a reward function**. But how we can scale that in big and complex environments?
## So what is Curiosity?
A solution to these problems is **to develop a reward function intrinsic to the agent, i.e., generated by the agent itself**. The agent will act as a self-learner since it will be the student and its own feedback master.
**This intrinsic reward mechanism is known as Curiosity** because this reward pushes the agent to explore states that are novel/unfamiliar. To achieve that, our agent will receive a high reward when exploring new trajectories.
This reward is inspired by how humans act. ** We naturally have an intrinsic desire to explore environments and discover new things**.
There are different ways to calculate this intrinsic reward. The classical approach (Curiosity through next-state prediction) is to calculate Curiosity **as the error of our agent in predicting the next state, given the current state and action taken**.
<img src="https://huggingface.co/datasets/huggingface-deep-rl-course/course-images/resolve/main/en/unit5/curiosity3.png" alt="Curiosity"/>
Because the idea of Curiosity is to **encourage our agent to perform actions that reduce the uncertainty in the agent’s ability to predict the consequences of its actions** (uncertainty will be higher in areas where the agent has spent less time or in areas with complex dynamics).
If the agent spends a lot of time on these states, it will be good at predicting the next state (low Curiosity). On the other hand, if it’s in a new, unexplored state, it will be hard to predict the following state (high Curiosity).
<img src="https://huggingface.co/datasets/huggingface-deep-rl-course/course-images/resolve/main/en/unit5/curiosity4.png" alt="Curiosity"/>
Using Curiosity will push our agent to favor transitions with high prediction error (which will be higher in areas where the agent has spent less time, or in areas with complex dynamics) and **consequently better explore our environment**.
There’s also **other curiosity calculation methods**. ML-Agents uses a more advanced one called Curiosity through random network distillation. This is out of the scope of the tutorial but if you’re interested [I wrote an article explaining it in detail](https://medium.com/data-from-the-trenches/curiosity-driven-learning-through-random-network-distillation-488ffd8e5938).
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hf_public_repos/deep-rl-class/units/en | hf_public_repos/deep-rl-class/units/en/unit5/snowball-target.mdx | # The SnowballTarget Environment
<img src="https://huggingface.co/datasets/huggingface-deep-rl-course/course-images/resolve/main/en/unit7/snowballtarget.gif" alt="SnowballTarget"/>
SnowballTarget is an environment we created at Hugging Face using assets from [Kay Lousberg](https://kaylousberg.com/). We have an optional section at the end of this Unit **if you want to learn to use Unity and create your environments**.
## The agent's Goal
The first agent you're going to train is called Julien the bear 🐻. Julien is trained **to hit targets with snowballs**.
The Goal in this environment is that Julien **hits as many targets as possible in the limited time** (1000 timesteps). It will need **to place itself correctly in relation to the target and shoot**to do that.
In addition, to avoid "snowball spamming" (aka shooting a snowball every timestep), **Julien has a "cool off" system** (it needs to wait 0.5 seconds after a shoot to be able to shoot again).
<figure>
<img src="https://huggingface.co/datasets/huggingface-deep-rl-course/course-images/resolve/main/en/unit7/cooloffsystem.gif" alt="Cool Off System"/>
<figcaption>The agent needs to wait 0.5s before being able to shoot a snowball again</figcaption>
</figure>
## The reward function and the reward engineering problem
The reward function is simple. **The environment gives a +1 reward every time the agent's snowball hits a target**. Because the agent's Goal is to maximize the expected cumulative reward, **it will try to hit as many targets as possible**.
<img src="https://huggingface.co/datasets/huggingface-deep-rl-course/course-images/resolve/main/en/unit7/snowballtarget_reward.png" alt="Reward system"/>
We could have a more complex reward function (with a penalty to push the agent to go faster, for example). But when you design an environment, you need to avoid the *reward engineering problem*, which is having a too complex reward function to force your agent to behave as you want it to do.
Why? Because by doing that, **you might miss interesting strategies that the agent will find with a simpler reward function**.
In terms of code, it looks like this:
<img src="https://huggingface.co/datasets/huggingface-deep-rl-course/course-images/resolve/main/en/unit7/snowballtarget-reward-code.png" alt="Reward"/>
## The observation space
Regarding observations, we don't use normal vision (frame), but **we use raycasts**.
Think of raycasts as lasers that will detect if they pass through an object.
<figure>
<img src="https://huggingface.co/datasets/huggingface-deep-rl-course/course-images/resolve/main/en/unit5/raycasts.png" alt="Raycasts"/>
<figcaption>Source: <a href="https://github.com/Unity-Technologies/ml-agents">ML-Agents documentation</a></figcaption>
</figure>
In this environment, our agent has multiple set of raycasts:
<img src="https://huggingface.co/datasets/huggingface-deep-rl-course/course-images/resolve/main/en/unit7/snowball_target_raycasts.png" alt="Raycasts"/>
In addition to raycasts, the agent gets a "can I shoot" bool as observation.
<img src="https://huggingface.co/datasets/huggingface-deep-rl-course/course-images/resolve/main/en/unit7/snowballtarget-obs-code.png" alt="Obs"/>
## The action space
The action space is discrete:
<img src="https://huggingface.co/datasets/huggingface-deep-rl-course/course-images/resolve/main/en/unit7/snowballtarget_action_space.png" alt="Action Space"/>
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hf_public_repos/deep-rl-class/units/en | hf_public_repos/deep-rl-class/units/en/unit5/conclusion.mdx | # Conclusion
Congrats on finishing this unit! You’ve just trained your first ML-Agents and shared it to the Hub 🥳.
The best way to learn is to **practice and try stuff**. Why not try another environment? [ML-Agents has 18 different environments](https://github.com/Unity-Technologies/ml-agents/blob/develop/docs/Learning-Environment-Examples.md).
For instance:
- [Worm](https://singularite.itch.io/worm), where you teach a worm to crawl.
- [Walker](https://singularite.itch.io/walker), where you teach an agent to walk towards a goal.
Check the documentation to find out how to train them and to see the list of already integrated MLAgents environments on the Hub: https://github.com/huggingface/ml-agents#getting-started
<img src="https://huggingface.co/datasets/huggingface-deep-rl-course/course-images/resolve/main/en/unit5/envs-unity.jpeg" alt="Example envs"/>
In the next unit, we're going to learn about multi-agents. You're going to train your first multi-agents to compete in Soccer and Snowball fight against other classmate's agents.
<img src="https://huggingface.co/datasets/huggingface-deep-rl-course/course-images/resolve/main/en/unit7/snowballfight.gif" alt="Snownball fight"/>
Finally, we would love **to hear what you think of the course and how we can improve it**. If you have some feedback then please 👉 [fill this form](https://forms.gle/BzKXWzLAGZESGNaE9)
### Keep Learning, stay awesome 🤗
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hf_public_repos/deep-rl-class/units/en | hf_public_repos/deep-rl-class/units/en/unit5/pyramids.mdx | # The Pyramid environment
The goal in this environment is to train our agent to **get the gold brick on the top of the Pyramid. To do that, it needs to press a button to spawn a Pyramid, navigate to the Pyramid, knock it over, and move to the gold brick at the top**.
<img src="https://huggingface.co/datasets/huggingface-deep-rl-course/course-images/resolve/main/en/unit7/pyramids.png" alt="Pyramids Environment"/>
## The reward function
The reward function is:
<img src="https://huggingface.co/datasets/huggingface-deep-rl-course/course-images/resolve/main/en/unit7/pyramids-reward.png" alt="Pyramids Environment"/>
In terms of code, it looks like this
<img src="https://huggingface.co/datasets/huggingface-deep-rl-course/course-images/resolve/main/en/unit7/pyramids-reward-code.png" alt="Pyramids Reward"/>
To train this new agent that seeks that button and then the Pyramid to destroy, we’ll use a combination of two types of rewards:
- The *extrinsic one* given by the environment (illustration above).
- But also an *intrinsic* one called **curiosity**. This second will **push our agent to be curious, or in other terms, to better explore its environment**.
If you want to know more about curiosity, the next section (optional) will explain the basics.
## The observation space
In terms of observation, we **use 148 raycasts that can each detect objects** (switch, bricks, golden brick, and walls.)
<img src="https://huggingface.co/datasets/huggingface-deep-rl-course/course-images/resolve/main/en/unit7/pyramids_raycasts.png"/>
We also use a **boolean variable indicating the switch state** (did we turn on or off the switch to spawn the Pyramid) and a vector that **contains the agent’s speed**.
<img src="https://huggingface.co/datasets/huggingface-deep-rl-course/course-images/resolve/main/en/unit7/pyramids-obs-code.png" alt="Pyramids obs code"/>
## The action space
The action space is **discrete** with four possible actions:
<img src="https://huggingface.co/datasets/huggingface-deep-rl-course/course-images/resolve/main/en/unit7/pyramids-action.png" alt="Pyramids Environment"/>
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hf_public_repos/deep-rl-class/units/en | hf_public_repos/deep-rl-class/units/en/live1/live1.mdx | # Live 1: How the course work, Q&A, and playing with Huggy
In this first live stream, we explained how the course work (scope, units, challenges, and more) and answered your questions.
And finally, we saw some LunarLander agents you've trained and play with your Huggies 🐶
<Youtube id="JeJIswxyrsM" />
To know when the next live is scheduled **check the discord server**. We will also send **you an email**. If you can't participate, don't worry, we record the live sessions. | 0 |