Author: Bas Hamstra
Date: 01:32:02 04/11/02
Go up one level in this thread
On April 10, 2002 at 18:01:23, Robert Hyatt wrote: >On April 10, 2002 at 16:38:49, Gian-Carlo Pascutto wrote: > >>On April 10, 2002 at 00:27:54, Keith Evans wrote: >> >>>When Hsu designed the move generator for Deep Blue he added extra hardware so >>>that he could generate checking (even discovered checks) and check evasion moves >>>more quickly than his first move generator could. (Compare the diagrams for the >>>square transmitters and receivers in the IEEE micro article to those in his >>>thesis and to those describing the Belle generator.) He could have generated >>>these moves without the extra hardware and design time by iterating through >>>moves and throwing away moves which didn't meet the criteria, but apparently he >>>thought that the performance of the move generator was important enough in these >>>cases to justify adding the complexity. >>> >>>What's the general opinion on this? Was this time well spent, or was it a waste >>>of time? I searched for information on what programs typically do during qsearch >>>and couldn't find much of anything directly related. It seems like he would have >>>simulated this before commiting to design, and perhaps discussed it publicly >>>with some top programmers. >> >>In the qsearch, being able to generate only capture moves fast is >>a nice speed advantage. If you want to do checks/check evasions too, >>you'll have to generate these moves somehow. If you have to fall >>back to your standard movegen, that'll come with a speed loss, so >>it makes sense to try to avoid that. >> >>Since qsearch tends to amount to a large % of the nodes searched, >>this sounds like an understandable decision. >> >>Note that there are usually a lot less captures+checks/evasions than >>normal moves. >> >>-- >>GCP > > >we did that in Cray Blitz... But in Crafty I dumped the big q-search early >on (version 13 I think) and went to a simpler q-search with a more complex >base search... The checks in q-search find some cute things, of course. But >they also miss a lot. > >I don't do it at present because the q-search is highly selective anyway, >and it has significant errors present in it. Trying to make something that >has lots of known errors in it even bigger seems (to me) to be inviting >trouble. > >I occasionally miss a tactic that the old q-search would see. I also find >a tactic that the more accurate search finds that the old one missed. I have >not (yet) been unsatisfied... > >The main thing checks in the q-search helps to find are the mates in 30 and >so forth that rarely happen in real games... > >IE I have seen chessmaster do a 4 ply search in 4 minutes, and get totally >creamed by a simple positional trap, because it was following checks out to >impossible depths. Of course, Crafty does the opposite as well, by missing a >very deep tactic due to the simple q-search. But since I see no advantage in >either approach, I like "simple is better". :) Sounds reasonable. However I saw you complain many times about nullmove hiding many mate threats. Well, that IS related. With such a mini qsearch you create dangerous blind spots. Question is are you willing to sacrifice a little positional depth to get rid of those blind spots. Personally I am. Best regards, Bas.
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