Answers.Body: <p>I think that in the case of the immediate ...Rxg5, Stockfish has seen one move deeper than in the version with ...Rg6 first. As a result the evaluation is slightly different - 0.1 less, in this case. So it ranks ...Rg6 first. It doesn't really matter either way, it's just an artifact of how engines work.</p>
  <p>Same for ...e1=B+. It gets captured immediately, so it's effectively the same move as ...e1=Q+ that would also be captured immediately. Which one it happens to show is essentially random, it doesn't have a builtin preference for promoting to a queen in cases where it doesn't matter at all.</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2022-11-03T12:11:45.783Z
Answers.LastActivityDate: 2022-11-03T12:11:45.783Z
Answers.UserDisplayName: RemcoGerlich
Answers.Body: <p>No particular reason. Note the scores, <code>-8.9</code> and <code>-8.8</code>, practically indistinguishable. Stockfish simply saw the same sequence of tactical response with and without the move <code>...Rg6</code>. The line <code>...Rg6</code> came first due to random fluctuation.</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2022-11-03T20:51:08.803Z
Answers.Text: FWIW, a human player might play the slower version to have a little more time on their clock.
Answers.UserDisplayName: Philip Roe
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2022-11-03T10:38:44.863Z
Answers.LastActivityDate: 2022-11-03T10:38:44.863Z
Answers.UserDisplayName: SmallChess
Body: <p>The FEN is:</p>
  <pre><code>r2qk1r1/ppp2p1p/2n1bn1Q/4p1B1/8/2P4P/PP1NpKP1/R5NR b kq - 0 1
  </code></pre>
  <p><img src="https://i.sstatic.net/hJjNV.jpg" alt="engine" /></p>
  <p>Clearly black is winning because the white bishop can be captured (with a discovery available if white recaptures). However, the stockfish eval seems strange - why would it suggest that playing an intermediate Rg6 is better? The continuation is Qh4 Rxg5 Qxg5 anyway, which is just a slower way to do the same thing. Wouldn't it be better to play the most direct move Rxg5?</p>
  <p>Then I am also confused about the 3rd recommendation of e1=B+, why would it suggest to underpromote there?</p>
  
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2022-11-26T11:41:12.870Z
Comments.Text: -8.8 and -8.9 are basically the same evaluation
Comments.UserDisplayName: David
Tags: <stockfish><evaluation><pawn-promotion>
Title: Why does stockfish make these strange recommendations?
ThreadText: # Why does stockfish make these strange recommendations?
  
  (Asked by: username_0 on 2022-11-03)
  
  The FEN is:
  
  ```
  r2qk1r1/ppp2p1p/2n1bn1Q/4p1B1/8/2P4P/PP1NpKP1/R5NR b kq - 0 1
  
  ```
  
  ![engine](https://i.sstatic.net/hJjNV.jpg)
  
  Clearly black is winning because the white bishop can be captured (with a discovery available if white recaptures). However, the stockfish eval seems strange - why would it suggest that playing an intermediate Rg6 is better? The continuation is Qh4 Rxg5 Qxg5 anyway, which is just a slower way to do the same thing. Wouldn't it be better to play the most direct move Rxg5?
  
  Then I am also confused about the 3rd recommendation of e1=B+, why would it suggest to underpromote there?
  
  **Tags:** stockfish, evaluation, pawn-promotion
  
  > **Comments:**
  > **username_1**: -8.8 and -8.9 are basically the same evaluation  
  
  ---
  
  ## 2 answers
  
  ### Answer by username_2 on 2022-11-03. Score: 3 | Accepted answer
  
  I think that in the case of the immediate ...Rxg5, Stockfish has seen one move deeper than in the version with ...Rg6 first. As a result the evaluation is slightly different - 0.1 less, in this case. So it ranks ...Rg6 first. It doesn't really matter either way, it's just an artifact of how engines work.
  
  Same for ...e1=B+. It gets captured immediately, so it's effectively the same move as ...e1=Q+ that would also be captured immediately. Which one it happens to show is essentially random, it doesn't have a builtin preference for promoting to a queen in cases where it doesn't matter at all.
  
  
  ---
  
  ### Answer by username_3 on 2022-11-03. Score: 7
  
  No particular reason. Note the scores, `-8.9` and `-8.8`, practically indistinguishable. Stockfish simply saw the same sequence of tactical response with and without the move `...Rg6`. The line `...Rg6` came first due to random fluctuation.
  
  > **Comments:**
  > **username_4**: FWIW, a human player might play the slower version to have a little more time on their clock.  
  
  ---
  
  