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Mythbuster continued
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Vincent Diepeveen



Joined: 09 Mar 2006
Posts: 1738
Location: The Netherlands
PostPost subject: Re: Mythbuster continued ...    Posted: Sun Mar 18, 2012 4:29 pm Reply to topic Reply with quote
beram wrote:
Another game where Houdini lets Komodo come away with a draw from a lost position. After This time it was in game 56
[D]7Q/8/3kpPp1/8/5n2/2P2PK1/1p6/1r6 b - - 0 49
   ::    ::    ::    WQ
::    ::    ::    ::    
   ::    BK BP WP BP ::
::    ::    ::    ::    
   ::    ::    BN    ::
::    WP    :: WP WK    
   BP    ::    ::    ::
:: BR ::    ::    ::    

after 49. ..Rg1 it is a draw, as Stockfish very quick and Komodo rather quickly see. Deep Rybka w32 on slow laptop after 6 minutes at depth 19 switches to Nh5.
Houdini 1.5a fails to find the winning move Nh5+! within reasonable time after depth 31 still it prefers Rg1 which is a draw as Komodo shows in his eval in the game.pgn just one move later after playing Kxf4

any explanations someone ?


Yeah the problem is the fact they just check a very narrow mainline, so if their first predicted move is some pawns difference, then huge problem occurs, as all pruning reduces the search tree a lot when material differences are there compared to the mainline.

So for example when you follow mainline and it gives +0.00 and some other line initially is +5 for white, then there is a material difference. The megapruning gets to effect and reduces all search lines bigtime, so checking Nh5 deeply isn't what happens, instead it prunes it so bigtime that it just can't find the win for it.

Similar effect is when first move is mispredicted. So it plays a move,
it expects move Y, instead move Z is best. Move Z it reduces heavily the search lines. Easily to less than half the depth it shows, and it just won't see much there.

All your examples show this clearly both for komodo as well as houdini, it's a common problem in todays computerchess.

In 1999 when i toyed with reductions myself, i couldn't get it stable for Diep; the bad side effects were worse than the benefit, as the nodes per second wasn't high yet of Diep. The world c hamps 1999 version of Diep used reductions; that's why in endgame it outsearched everyone so bigtime, even though it just got 70k nps or so at Bob's quad Xeon 400, versus others millions of nps.

In todays high nps game, this search depth difference is even bigger, just because they go easily through tactical barrier in any line, the reductions work and the worst case behaviour of them is more acceptable, even though it lets them miss weird things as you show.

Note that it's not just reductions in case of houdini + SF that cause this. The razoring + futility + bigger reduction factor in nullmove strengthens these effects.

Around 1995-1996 i was the first one to describe on RGCC the combination of using different R's together for nullmove. It's interesting to see how it seems to work over 10 years later for most of todays chess engines.
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Display posts from previous:   
Subject Author Date/Time
Mythbuster continued Bram Mourik Thu Mar 08, 2012 8:03 pm
      Re: I have a recommendation for you and all testers Jorge Pichard Fri Mar 09, 2012 12:42 am
            Re: I have a recommendation for you and all testers Matthias Gemuh Fri Mar 09, 2012 6:04 am
                  Re: I have a recommendation for you and all testers Ingo Bauer Fri Mar 09, 2012 6:19 am
                        Re: I have a recommendation for you and all testers Timo Klaustermeyer Fri Mar 09, 2012 6:40 am
                              Re: I have a recommendation for you and all testers Ingo Bauer Fri Mar 09, 2012 7:30 am
      Re: Mythbuster continued Bram Mourik Fri Mar 09, 2012 7:13 am
            Re: Mythbuster continued Jouni Uski Fri Mar 09, 2012 7:39 am
                  Re: Mythbuster continued ...but Komodo comes back Bram Mourik Fri Mar 09, 2012 9:39 pm
                        Re: Mythbuster continued ...but Komodo comes back Timo Klaustermeyer Sat Mar 10, 2012 12:18 am
                              Re: Mythbuster continued ...but Komodo comes back Bram Mourik Sat Mar 10, 2012 4:55 pm
                                    Re: Mythbuster continued ...but Komodo comes back Jouni Uski Sat Mar 10, 2012 5:35 pm
                                          Re: Mythbuster continued ...but Komodo comes back Timo Klaustermeyer Sun Mar 11, 2012 12:30 am
                                    Re: Mythbuster continued ...but Komodo comes back Timo Klaustermeyer Sun Mar 11, 2012 12:02 am
                                          Re: Mythbuster continued ...but Komodo comes back Jorge Pichard Sun Mar 11, 2012 11:34 am
                                          Re: Mythbuster continued ...but Komodo comes back Bram Mourik Sun Mar 11, 2012 7:15 pm
                                                Re: Mythbuster continued ...but Komodo comes back Timo Klaustermeyer Mon Mar 12, 2012 8:04 am
                                                      Re: Mythbuster continued ...but Komodo comes back Bram Mourik Mon Mar 12, 2012 6:15 pm
                                                            Re: Mythbuster continued ...but Komodo comes back Jorge Pichard Tue Mar 13, 2012 12:51 am
                                                                  Re: Mythbuster continued ...but Komodo comes back Jouni Uski Tue Mar 13, 2012 11:17 am
                                                                        Re: Mythbuster continued ...but Komodo comes back Bram Mourik Wed Mar 14, 2012 7:46 pm
                                                                              Re: Mythbuster continued ...but Komodo comes back Jouni Uski Wed Mar 14, 2012 8:52 pm
                                                                                    Re: Mythbuster continued ...but Komodo comes back Dr.Wael Deeb Thu Mar 15, 2012 9:11 am
                                                                                          Re: Mythbuster continued ...but Komodo comes back Maurizio Maglio Fri Mar 16, 2012 9:35 pm
                                                                                          Re: Mythbuster continued ...but Komodo comes back Dr.Wael Deeb Sat Mar 17, 2012 9:22 am
                                                                                          Re: Mythbuster continued ... Bram Mourik Sun Mar 18, 2012 4:19 pm
                                                                                          Re: Mythbuster continued ... Vincent Diepeveen Sun Mar 18, 2012 4:29 pm
                                                                                          Re: Mythbuster continued ... Bram Mourik Sun Mar 18, 2012 4:41 pm
                                                                                          Re: Mythbuster continued ... Robert Houdart Sun Mar 18, 2012 4:52 pm
                                                                                          Re: Mythbuster continued ... Bram Mourik Sun Mar 18, 2012 5:03 pm
                                                                                    Re: Mythbuster continued ...but Komodo comes back Bram Mourik Fri Mar 16, 2012 7:00 pm
                                                                                          Re: Mythbuster continued ...but Komodo comes back Robert Houdart Fri Mar 16, 2012 7:27 pm
                                                                                          Re: Mythbuster continued ...but Komodo comes back Timo Klaustermeyer Fri Mar 16, 2012 9:42 pm
                                                                                          Re: Mythbuster continued ...but Komodo comes back Maurizio Maglio Fri Mar 16, 2012 9:49 pm
                                                      Re: Mythbuster continued ...but Komodo comes back Jorge Pichard Tue Mar 13, 2012 12:47 am
                                                      Re: Mythbuster continued ...Houdini likes it French way Bram Mourik Wed Mar 14, 2012 5:05 pm
                                                            Re: Mythbuster continued ...Houdini likes it French way Timo Klaustermeyer Wed Mar 14, 2012 7:35 pm
      Re: Mythbuster conclusions Bram Mourik Mon Mar 19, 2012 6:28 pm
            Re: Mythbuster conclusions Timo Klaustermeyer Mon Mar 19, 2012 11:37 pm
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