Author: Robert Hyatt
Date: 15:01:23 04/10/02
Go up one level in this thread
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". :)
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