Author: Ricardo Gibert
Date: 03:34:40 10/05/00
Go up one level in this thread
On October 05, 2000 at 00:07:49, Robert Hyatt wrote: >On October 04, 2000 at 12:57:25, Ricardo Gibert wrote: > >>On October 04, 2000 at 12:04:01, Mike Adams wrote: >> >>>>I'm sure there is some truth to what you are saying, but if Crafty needs to >>>>search to a greater depth to find the same tactics, isn't that a sign of some >>>>type of inefficiency? >>> >>> I've noticed that some things speed up search a lot while compromising the >>>integrity of the idea of a pure search. Move ordering doesnt do this normally. >>>If you search every node with simple Min Max or NegaMax it will be really slow >>>but you will see everything up to the depth you search. Now if you include alpha >>>beta and some move ordering like order like capture it will be much quicker and >>>just as reliable. You'll get the same depth but faster. Now say you were >>>getting depht 5, Now you add Null Move and Futility Pruning. Both these >>>algorithms are to put it simply ways of finding out if certain parts of the tree >>>get lower scores and therefor are not worth searching. Now your no longer >>>searching everything. You're making estimates. Lets say this brings you from >>>depth 5 to depth 7. Well its no longer a pure depth 7 search as you would have >>>had if you searched every postion. Sometimes the result of this 'estimated >>>search' will vary from a pure search. Well here is how I look at it. In many >>>situations your 'estimated search' is good enought and your getting 2 extra >>>depth. In some situations you miss things that you would have seen with a pure >>>search at an earlier depth tell later. But that can be ok. lets say a depth 5 >>>tactic doesnt appear untill depth 7 with 'estimated search'. Well if you did a >>>pure search you would have got depth 5 and seen it. With the 'estimated search' >>>you got depth 7 and finnaly saw it. As long as the extra depth required is not >>>more than the gains from the 'estimates search' you really havent lost much. And >>>often in the cases were things take longer to find it is the case that you'll >>>still find whatever you would have found with the full search. Now lets say a >>>tactic should show up at depth 5 you're getting depth 7 with this 'estimated >>>search' and you miss the tactic because you need depht 8 or 9. Then you lose but >>>from what i have seen with Pulsar it is much better to cut off the bad lines and >>>get the deeper search than it is to be cautious and do a pure search every time. >> >>Alphabeta and futility pruning are theoretically sound so you can search deeper >>without sacrificing soundness, while nullmove (a form of selective search) >>involves making a tradeoff albeit an effective one. > > >No forward pruning is completely "sound". Futility pruning is no exception. >It can work well. And it can produce wrong answers. Which is why I no longer >use it. Chesswise you are certainly right. That's the relevant context here.
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