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For Marco---possible Stockfish bug
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Evert Glebbeek



Joined: 21 Jan 2011
Posts: 862
Location: NL
PostPost subject: Re: For Marco---possible Stockfish bug    Posted: Fri Feb 03, 2012 2:41 pm Reply to topic Reply with quote
lech wrote:
s mean?
If an item returns VALUE_DRAW it is very likely (repeated moves) that a lot of nodes return a bad value and move, they will have VALUE_DRAW as beta.
This is very wrong.

Why?
Once the position repeats (for the third time) the game ends and the node is a terminal node. The results is a draw. So what it says that the repeated move leads to a draw, which is correct.
If the current search bounds say that this is a good result (raises alpha), then it means that we currently expect our position to be worse. If it fails high (raises alpha >= beta) then it is the best option found so far. What we know at that point is that this line is at least a draw, but we don't have an exact score, only a lower bound. If we need an exact score (for a PV node) then the position will be researched with a wider window. Now, the draw score will not cause a cutoff and we can try to find something better (we may or may not).

Of course there is a problem if the evaluation scores a better position as worse, even marginally worse, because then the engine needlessly goes for a repetition. The correct fix is to improve the evaluation. A workaround is to set a contempt factor that makes the engine not accept the repetition until the evaluation is below a certain limit, so it doesn't go for the draw in positions that are only marginally worse (or where it still has some prospect of winning the game).
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Subject Author Date/Time
For Marco---possible Stockfish bug Louis Zulli Tue Jan 31, 2012 5:49 pm
      Re: For Marco---possible Stockfish bug Marco Costalba Tue Jan 31, 2012 7:12 pm
      Re: For Marco---possible Stockfish bug Joona Kiiski Wed Feb 01, 2012 7:56 am
            Re: For Marco---possible Stockfish bug Marek Kwiatkowski Wed Feb 01, 2012 10:02 am
                  Re: For Marco---possible Stockfish bug Joona Kiiski Wed Feb 01, 2012 12:48 pm
                        Re: For Marco---possible Stockfish bug Louis Zulli Wed Feb 01, 2012 2:41 pm
                              Re: For Marco---possible Stockfish bug Marek Kwiatkowski Wed Feb 01, 2012 7:15 pm
                                    Re: For Marco---possible Stockfish bug Marco Costalba Wed Feb 01, 2012 7:23 pm
                                          Re: For Marco---possible Stockfish bug Marek Kwiatkowski Wed Feb 01, 2012 9:05 pm
                                    Re: For Marco---possible Stockfish bug Joona Kiiski Wed Feb 01, 2012 8:32 pm
                                          Re: For Marco---possible Stockfish bug Marek Kwiatkowski Wed Feb 01, 2012 9:02 pm
                                                Re: For Marco---possible Stockfish bug Joona Kiiski Thu Feb 02, 2012 8:30 am
                                                      Re: For Marco---possible Stockfish bug Marek Kwiatkowski Thu Feb 02, 2012 8:36 am
                                                            Re: For Marco---possible Stockfish bug Joona Kiiski Thu Feb 02, 2012 10:52 am
                                                                  Re: For Marco---possible Stockfish bug Marek Kwiatkowski Thu Feb 02, 2012 2:08 pm
                                                                        Re: For Marco---possible Stockfish bug Joona Kiiski Thu Feb 02, 2012 3:45 pm
                                                                              Re: For Marco---possible Stockfish bug Marek Kwiatkowski Thu Feb 02, 2012 5:32 pm
                                                                                    Re: For Marco---possible Stockfish bug david nash Thu Feb 02, 2012 6:14 pm
                                                                                    Re: For Marco---possible Stockfish bug Richard Vida Thu Feb 02, 2012 7:23 pm
                                                                                          Re: For Marco---possible Stockfish bug Marco Costalba Thu Feb 02, 2012 8:04 pm
                                                                                          Re: For Marco---possible Stockfish bug Robert Wagner Campos Thu Feb 02, 2012 8:59 pm
                                                                                          Re: For Marco---possible Stockfish bug Uri Blass Thu Feb 02, 2012 10:41 pm
                                                                                          Re: For Marco---possible Stockfish bug Marek Kwiatkowski Thu Feb 02, 2012 9:01 pm
                                                                                          Re: For Marco---possible Stockfish bug Sven Schüle Thu Feb 02, 2012 11:28 pm
                                                                                          Re: For Marco---possible Stockfish bug Robert Wagner Campos Fri Feb 03, 2012 12:26 pm
                                                                                          Re: For Marco---possible Stockfish bug Uri Blass Fri Feb 03, 2012 2:14 pm
                                                                                          Re: For Marco---possible Stockfish bug Marek Kwiatkowski Fri Feb 03, 2012 2:21 pm
                                                                                          Re: For Marco---possible Stockfish bug Evert Glebbeek Fri Feb 03, 2012 2:41 pm
                                                                                          Re: For Marco---possible Stockfish bug Marek Kwiatkowski Fri Feb 03, 2012 2:58 pm
                                                                                          Re: For Marco---possible Stockfish bug Sam Hamilton Fri Feb 03, 2012 3:23 pm
                                                                                          Re: For Marco---possible Stockfish bug Evert Glebbeek Sat Feb 04, 2012 7:07 am
                                                                                          Re: For Marco---possible Stockfish bug Marek Kwiatkowski Sat Feb 04, 2012 9:31 am
                                                                                          Re: For Marco---possible Stockfish bug Marek Kwiatkowski Sun Feb 05, 2012 4:20 pm
                                                                                          Re: For Marco---possible Stockfish bug Marek Kwiatkowski Sun Feb 05, 2012 5:24 pm
                                                                                          Re: For Marco---possible Stockfish bug Marek Kwiatkowski Wed Feb 08, 2012 1:54 pm
                                                                                          Re: For Marco---possible Stockfish bug Joerg Oster Wed Feb 08, 2012 5:14 pm
                                                                                          Re: For Marco---possible Stockfish bug Marek Kwiatkowski Wed Feb 08, 2012 5:49 pm
                                                                                          Re: For Marco---possible Stockfish bug Marek Kwiatkowski Sun Feb 19, 2012 5:37 pm
                                                                                          Re: For Marco---possible Stockfish bug Robert Wagner Campos Fri Feb 03, 2012 6:33 pm
                                                                                          Re: For Marco---possible Stockfish bug Robert Wagner Campos Fri Feb 03, 2012 6:15 pm
                                                                                          Re: For Marco---possible Stockfish bug Louis Zulli Sat Feb 04, 2012 1:50 am
                                                Re: For Marco---possible Stockfish bug Marek Kwiatkowski Fri Feb 03, 2012 2:08 pm
                                                      Re: For Marco---possible Stockfish bug Kevin Hearn Fri Feb 03, 2012 3:49 pm
                                                            Re: For Marco---possible Stockfish bug Marek Kwiatkowski Fri Feb 03, 2012 6:45 pm
                              Re: For Marco---possible Stockfish bug Joerg Oster Wed Feb 01, 2012 8:38 pm
                                    Re: For Marco---possible Stockfish bug Louis Zulli Wed Feb 01, 2012 9:14 pm
                                          Re: For Marco---possible Stockfish bug Joerg Oster Thu Feb 02, 2012 7:23 am
                                                Re: For Marco---possible Stockfish bug Marek Kwiatkowski Thu Feb 02, 2012 8:29 am
                                    Re: For Marco---possible Stockfish bug Louis Zulli Wed Feb 01, 2012 9:38 pm
                                          Re: For Marco---possible Stockfish bug Marek Kwiatkowski Wed Feb 01, 2012 9:54 pm
                                                Re: For Marco---possible Stockfish bug Louis Zulli Wed Feb 01, 2012 11:05 pm
                                                      Re: For Marco---possible Stockfish bug Marek Kwiatkowski Wed Feb 01, 2012 11:11 pm
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