Fix terminal Q-value in QLearningAgent/SARSA (use r, not r1) (#1247)#1337
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On entering a previously-terminal state, the agent set Q[s, None] = r1 (the reward of the *new* percept) instead of r (the stored reward received at the terminal state), per AIMA Fig 21.8 (Q[s, None] <- r). This made terminal Q-values wrong (e.g. ~-0.04 / noisy instead of +1/-1) and yielded incorrect policies. Verified: terminal Q-values now converge to ~+1 / ~-1. Fixes #1247.
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QLearningAgent (and SARSALearningAgent) set Q[s, None] = r1 (the new percept's reward) when the previous state was terminal, instead of r (the reward received at the terminal state) as in AIMA Fig 21.8. This made terminal Q-values wrong (≈-0.04/noisy instead of +1/-1) and produced incorrect policies. Fixed both; verified terminal Q-values now converge to ≈+1/-1 and the q-learning test passes. Fixes #1247.