Author: martin fierz
Date: 05:42:28 08/12/04
Go up one level in this thread
On August 12, 2004 at 08:38:46, martin fierz wrote: >On August 12, 2004 at 07:12:08, Tord Romstad wrote: > >>On August 12, 2004 at 06:40:48, Ross Boyd wrote: >> >>>Be careful with R=3. It has the potential to make your engine go blind. I lost >>>~50 (!!) elo when using pure R=3 in TRACE. I ran the experiment again two days >>>ago and it confirmed my previous findings. Currently, pure R=2 works best for >>>me... fewer OTB blunders. >> >>Like virtually everything else in computer chess, this is something which >>varies a lot between different engines. In my engine pure R=3 works >>*much* better than R=2, and slighly bettter than the classic adaptive >>null move pruning technique. Verified null move pruning also didn't >>work for me. The only improvement I have found over pure R=3 is a scheme >>were I occasionally use R=2 in positions where horizon effect problems >>are likely to be a problem (I use the eval to make the decision). >> >>Part of the reason that R=3 is best for me could be that my engine doesn't >>use null moves as much as most other engines. I only do a null move search >>when I am reasonably sure of a fail-high, but not quite sure enough to >>prune the whole subtree without search. Null move at all nodes more than >>doubles my node count, and does not increase the accuracy of my search >>noticably. >> >>Tord > >hi tord, > >i'm intrigued by your last sentence - that null move at all nodes more than >doubles your node count! i wonder how this is possible at all? why? if i >understand what you write you have an oracle which can tell you whether you >should do a null-move search at a given node or not. > >int alphabeta(....) grrr, hitting tab-return is not such a good idea :-) let me continue: you have int alphabeta(...) { ... if(null_oracle(position) == NULL_OK) do_nullmove_search() ... } if you remove that null_oracle thing you get twice as many nodes? i don't understand how that can happen. your null_oracle would basically be telling you not to do a null move search if it thinks it will fail low anyway. so for all nodes where you don't have to do a null move search with R=3 you have to do a normal search. you save yourself searching the R=3 part, but that should be very small compared to the normal search part, shouldn't it? what am i missing? cheers martin
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