Author: Andrew Wagner
Date: 17:21:01 06/15/04
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On June 15, 2004 at 20:09:48, Dann Corbit wrote: >On June 15, 2004 at 19:28:36, Andrew Wagner wrote: > >>I've heard it said before that it's not good to compare node counts between >>engines, and that node counts aren't a good indication of strength. So, I've >>been staying away from that a lot. >> >>The other day, I was chatting with my good friend Jaime Benito de Valle Ruiz. We >>see each other a lot on ICC and compare notes on our engines. We decided to play >>a fixed-depth game between our engines, to test eval strength. In the process of >>the game, he noticed that my node count was ridiculously higher than his. For >>example, in one position, where I was getting 277k nodes, he was getting like >>11k. Other engines varied, but no more than about 50k nodes. >> >>So we started doing some tests. For him, he got a huge node reduction by using >>some sophisticated aspiration windows. So, my question is three-fold: >> >>1.) Do most engines get a similarly large reduction in nodes by using aspiration >>windows? > >It will depend on what other things you are using to trim the tree. > >>2.) What other techniques reduce node counts at a fixed depth? > >A. Move ordering is the most important thing. So a good hash table is a must. >B. After that, null move reduction will be a stupendous node reducer. >C. PVS search does fewer nodes than ordinary Alpha-Beta >D. SEE is worth a lot for reduction >E. Razoring will reduce nodes, but you have to be careful not to shave the skin >off with the hair >F. IID will help, especially in deep searches >G. Aspiration window (mentioned above) reduces nodes. >H. Easy move cutoff > >Here are things that will cost you nodes, but are a good idea anyway: >A. Check extensions >B. Increasing quiescense depth (if you don't allow infinite quiescence) >C. Single reply extensions >D. Pawn race extensions >E. Recapture extensions > >Also, adding king safety and pawn structure to your evaluation will slow down >the NPS greatly, but make the program play better. > > > >>3.) To what extent are node counts reliable for determining engine strength? > >Not generally useful, except to compare against yourself. Goliath will be >around one million NPS on a machine where Yace will get 300K NPS. But they are >about the same strength. I should have been clearer. I didn't mean NPS, but number of nodes searched.
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