Answers.Body: <p>We're going to assume there is no hardware issue, as pointed by Tonny Ennis in his comment.</p>
  
  <p>It's possible that a computer engine experiences a "bad" tournament, but it's extremely rare. When we say "bad", we don't mean collapsing like blundering pieces, it's more like not getting a good position suitable for the engine. Computer engine always play at a constant strength, dictated by the algorithm. They won't do anything other than what the algorithm tells it to do.</p>
  
  <p>Let's give an example, it's well known Komodo is a better engine than Stockfish in a strategic position. If we randomly choose the openings in a match of four. We might see a closed position in three of those games. As expected, Komodo outplayed Stockfish in those three games. The final score would be 3-1 in favour of Komodo.</p>
  
  <p>Does that mean Komodo is a much stronger engine than Stockfish? Probably not. Can we conclude Stockfish had a "bad day"? Maybe. But please remember the sample size is <strong>too small</strong>, what if we let them play more games? A typical computer chess tournament can have a match with over 1000 games. If we do it, we might see a very different result.</p>
  
  <p>Conclusion: if we see a chess engine has a "bad day", usually it's because the sample size is <strong>too small</strong> or the testing condition is <strong>biased</strong>. The law of large number will erase unsystematic variation given enough sample size. </p>
  
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2015-06-19T22:55:57.310Z
Answers.Text: The question is whether the engine can have a bad day, given that the computers get to choose what opening they play.
Answers.UserDisplayName: limits
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Answers.CreationDate: 2015-06-20T06:22:26.270Z
Answers.Text: The answer does include that. If computers can choose openings and they have a "bad day", most likely you don't have enough sample size.
Answers.UserDisplayName: SmallChess
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2015-06-20T18:43:01.680Z
Answers.Text: I give you upvote, but the question is whether variation in playing strength will/can occur, not whether a large sample size will override variations.
Answers.UserDisplayName: limits
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2015-06-20T23:41:49.750Z
Answers.Text: But... Didn't I mention it can occur?
Answers.UserDisplayName: SmallChess
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2015-06-21T00:12:11.583Z
Answers.Text: Yes, you didn't explain why it is so.
Answers.UserDisplayName: limits
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2015-06-21T00:24:47.213Z
Answers.Text: Lacking of sufficient sample size is the common reason.
Answers.UserDisplayName: SmallChess
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2015-06-19T01:30:27.863Z
Answers.LastActivityDate: 2015-06-19T01:30:27.863Z
Answers.UserDisplayName: SmallChess
Body: <p>Tournament players can "have a good tournament" because of the psychology involved, so their playing strength will vary from game to game. Do computers play at a constant strength all the time, or do they have the occasional bad tournament?</p>
  
Comments.ContentLicense: CC BY-SA 3.0
Comments.CreationDate: 2015-06-19T01:13:20.903Z
Comments.Text: Back in the day of specialized custom hardware, a machine could 'have a bad day' when a component failed or perhaps when telecommunications were spotty. Not so common any more given that amazing machines are cheap.
Comments.UserDisplayName: Tony Ennis
Tags: <engines><tournament><computer-chess>
Title: Can a computer have a good tournament?
ThreadText: # Can a computer have a good tournament?
  
  (Asked by: username_0 on 2015-06-18)
  
  Tournament players can "have a good tournament" because of the psychology involved, so their playing strength will vary from game to game. Do computers play at a constant strength all the time, or do they have the occasional bad tournament?
  
  **Tags:** engines, tournament, computer-chess
  
  > **Comments:**
  > **username_1**: Back in the day of specialized custom hardware, a machine could 'have a bad day' when a component failed or perhaps when telecommunications were spotty. Not so common any more given that amazing machines are cheap.  
  
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  ## 1 answers
  
  ### Answer by username_2 on 2015-06-19. Score: 3 | Accepted answer
  
  We're going to assume there is no hardware issue, as pointed by Tonny Ennis in his comment.
  
  It's possible that a computer engine experiences a "bad" tournament, but it's extremely rare. When we say "bad", we don't mean collapsing like blundering pieces, it's more like not getting a good position suitable for the engine. Computer engine always play at a constant strength, dictated by the algorithm. They won't do anything other than what the algorithm tells it to do.
  
  Let's give an example, it's well known Komodo is a better engine than Stockfish in a strategic position. If we randomly choose the openings in a match of four. We might see a closed position in three of those games. As expected, Komodo outplayed Stockfish in those three games. The final score would be 3-1 in favour of Komodo.
  
  Does that mean Komodo is a much stronger engine than Stockfish? Probably not. Can we conclude Stockfish had a "bad day"? Maybe. But please remember the sample size is **too small**, what if we let them play more games? A typical computer chess tournament can have a match with over 1000 games. If we do it, we might see a very different result.
  
  Conclusion: if we see a chess engine has a "bad day", usually it's because the sample size is **too small** or the testing condition is **biased**. The law of large number will erase unsystematic variation given enough sample size.
  
  > **Comments:**
  > **username_0**: The question is whether the engine can have a bad day, given that the computers get to choose what opening they play.  
  > **username_2**: The answer does include that. If computers can choose openings and they have a "bad day", most likely you don't have enough sample size.  
  > **username_0**: I give you upvote, but the question is whether variation in playing strength will/can occur, not whether a large sample size will override variations.  
  > **username_2**: But... Didn't I mention it can occur?  
  > **username_0**: Yes, you didn't explain why it is so.  
  > **username_2**: Lacking of sufficient sample size is the common reason.  
  
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