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18 lines
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18 lines
1.2 KiB
Plaintext
# Mid-way Recap [[mid-way-recap]]
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Before diving into Q-Learning, let's summarize what we just learned.
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We have two types of value-based functions:
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- State-value function: outputs the expected return if **the agent starts at a given state and acts accordingly to the policy forever after.**
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- Action-value function: outputs the expected return if **the agent starts in a given state, takes a given action at that state** and then acts accordingly to the policy forever after.
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- In value-based methods, rather than learning the policy, **we define the policy by hand** and we learn a value function. If we have an optimal value function, we **will have an optimal policy.**
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There are two types of methods to learn a policy for a value function:
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- With *the Monte Carlo method*, we update the value function from a complete episode, and so we **use the actual accurate discounted return of this episode.**
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- With *the TD Learning method,* we update the value function from a step, so we replace \\(G_t\\) that we don't have with **an estimated return called TD target.**
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<img src="https://huggingface.co/datasets/huggingface-deep-rl-course/course-images/resolve/main/en/unit3/summary-learning-mtds.jpg" alt="Summary"/>
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