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I’m trying some practice games against Stockfish level eight. I always lose but sometimes Stockfish makes obviously bad moves and I get ahead. Here for example, Stockfish makes an inaccuracy followed by what seems to be an obvious blunder. I believe Stockfish level 8 is supposed to be ~2500 level, but I think a computer would avoid basic blunders. What causes such a misevaluation? enter image description here

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    Computers have no way to simulate how a 2500 rated human plays. It just mixes optimal moves with a random amount of terrible moves
    – David
    Commented May 24, 2021 at 21:17
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    but there’s no higher level! is stockfish set to always blunder some amount of the time?
    – curious
    Commented May 25, 2021 at 3:23
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    It would be very bad if Stockfish were programmed that way, though from your example it seems that it is clearly the case. A better way would be to make the AI have a centipawn loss distribution similar to what humans at that rating have. Contrary to what David says, it is definitely possible for a computer to simulate human players, even if it would be very complicated compared to just mimicking the centipawn loss distribution, which in turn is still far better than what you have observed.
    – user21820
    Commented May 25, 2021 at 5:12
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    @curious if Stockfish level 8 plays at 2500 strength, then there are indeed higher levels
    – David
    Commented May 25, 2021 at 8:44
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    @user21820 What do you mean by "centipawn loss distribution"? Distribution as a function of what? NB: People have tried experiments like Stockfish picking a lower option (but still high) than its top choice unless this costs a lot of eval. It didn't work, the engine is still invincible to humans. (Why? Because in most classical games, and almost all faster games, humans lose because of significantly weakening moves, not slightly suboptimal choices.) Commented May 25, 2021 at 19:09

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It must have been a bug. Lichess's Stockfish 8 has the following internal settings:

  • Skill level 20/20
  • Depth up to 22
  • Think up to 1000ms

I got the following information from the source code in Fishnet. Not sure how strong it is but definitely not a level that would drop a knight like this.

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  • What does "skill level" mean?
    – David
    Commented Aug 14, 2021 at 14:44
  • @David Stockfish has 20 AI levels. We call it "skill level" in computer chess.
    – SmallChess
    Commented Aug 15, 2021 at 17:34

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