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[Bram Mourik]

diep wrote:

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 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.

thx for answering, but as Stockfish I read is also such a big pruner, why than he finds Nh5 so quick ? just good first move luck ?