Author: Dann Corbit
Date: 17:09:48 06/15/04
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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.
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