Author: Ricardo Gibert
Date: 09:57:25 10/04/00
Go up one level in this thread
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.
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