Author: Eugene Nalimov
Date: 21:52:38 10/07/02
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Wrong. Today I visited the talk by Feng-Hsiung Hsu he gave at Microsoft. Here are some points from memory: They used forward pruning in the hardware, and according to Hsu it gives them 5x-10x speedup. He wrote about that in the book, too, but without any details. In the talk he named that pruning as "analogy cutoff" and mentioned that "if the move is useless in some position, it is also useless in the similar position". In the book he writes "it can be done in the hardware as long as it does not have to be 100% correct". They used null-move thread detection, as well as not only singular extension, but also extension on only 2 or 3 good replies. They used fractional extensions. He also says that their Q-search is much more powerful than the one that is usually used in the software-only programs. Hsu gave some details why they don't use null-move: (1) He thinks that singular extensions and null-move gave more-or-less the same rating difference (100-200 points IIRC). Null move allows you to search 3-4 plies deeper *everywhere*, but Hsu thinks that they have enough depth. He thinks that on the highest level it's absolutely necessary to analyze critical lines *much* deeper, and singular extensions do exactly that. (2) It's very hard to implement both null move and singular extensions in the same program. (3) When they played commercial programs that use null-move those programs regularly played themselves into zugzwang [by first pushing bad events over the horizon], and Hsu thinks that is direct result of the using null move. When asked by Tom, Hsu gave 2 examples of the search terms that are very expensive to evaluate: (1) Rooks on open file -- when they tried to analyze super-GM games, it looks that those GMs value rooks on the open file much less that usually thought. It happened that you need not only rook on the open file, you also need to be able control 7-th and 8-th rank (or is it file? sorry for my English). To properly calculate "will you control those ranks or not" you need lot of computing power. (2) King safety -- before castling they calculated 3 values (center, left, and right positions after castling), and to properly calculate control over those squares you need lot of power. [Note: here I disagree with Tom. Yes, those calculations can be done in the software, but assuming that there are ~20 such factors, and each slows the software search by ~10-20%, resulting 3x slowdown looks too much for me]. Thanks, Eugene On October 07, 2002 at 10:05:27, Gian-Carlo Pascutto wrote: >On October 06, 2002 at 21:21:17, Robert Hyatt wrote: > >>Lack of null-move is not a known deficiency. I can name a pretty successful >>program >>or two (commercial) that didn't rely on it... > >They use other ways of forward pruning that replace nullmove. The DB >team did nothing of that sorts. > >-- >GCP
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