Author: Dieter Buerssner
Date: 14:08:37 12/26/02
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On December 25, 2002 at 22:32:18, Robert Hyatt wrote: >Yes, but try it with best first ordering, which you can do after searching >the thing to 22 plies and finding the win. Just search to 22 plies again with >all the hash moves kept, but the scores cleared. No solution. This experiment would not prove the point (In the PV line, all black moves must be searched - also the very bad ones, that are easily refuted). This will (with fail-soft search) give many high scores in the HT. At the next depth, you can take advantage of those scores (which are even there with perfect move ordering). Some transpositions will be seen, that now can be forced in another line, but still the depth of the bad lines before can be more than enough (the new line is longer from the beginning). If you don't allow cutoffs (this is how I interprete "scores cleared" - how else should I interprete it), you have a different program, that does not take advantage of all this information. Note, that the later point is independent of the move ordering argument. I will try the experiment anyway at some time, but after looking fast over the code, I have seen, that for my engine it is not just a "change-few-lines-in-one-minute" experiment. Some small point about the "bad design, if it depends on move ordering". Some comments were given. Another subtle point is again the HTs. For many programs (I think including Crafty), the decision about extension/pruning will depend on the last move made. One example would be recapture. When you hit the HTs for a cutoff, most probably the last move in this line was different, then at the time, when you stored the position into the HTs. So, at this time, it is very possible, that you would search the different ancestors of this node with other search depth, than at the time it was stored. The consequences are, that this can introduce another "luck factor" . I believe, for most (if not all) rather good programs, pruning/extensions decisions depend on the window bounds (also in qsearch). It is quite obvious, that with different move ordering, you will hit positions with different bounds. You are certainly well aware of the fact, that similar things happen because of repetition detection and 50 moves rules. BTW. My "random move ordering" experiment for Fine 70 was done by disabling detection of repetition. Regards, Dieter
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