Author: Uri Blass
Date: 19:18:09 10/09/01
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On October 09, 2001 at 21:51:01, Dann Corbit wrote: >On October 09, 2001 at 21:26:54, Slater Wold wrote: >[snip] >>You would think. But it looks like TB's *might* be hindering the discovery of a >>quicker mate. > >For sure. When there are a lot of pieces on the board, chess programs will >simplify by trying direct exchanges. They will even toss a queen for *no >reason* except that it knows how to solve without the queen. > >Imagine that you have kqqqkr, and on the board we have kqqqqqKR. >The chess engine will very likely toss out two queens, if it sees a sure mate >using the kqqqkr tablebase. > >And why is it so hard to shake out of it? > >Because of alpha beta. One thing about Alpha-beta, it knows a bird in the hand >is worth two in the bush. If I have a mate in 35, and another path might put me >up 3 queens, it won't even consider the other path -- it will exit right away >because it sees: >If I chose door #1, I get a checkmate in 35 (value 32767-5) >If I choose door #2, I get a 3 queen advantage (value +30) >Therefore, choose door #1. Do not continue to search until the next iteration. >Also, if I have an advantage of a sure checkmate, any other choice will look >like a massive loser if it is not a shorter checkmate. You may be right and I think that the main reason is that programs use null move pruning and they may prune good lines after seeing mate. I am still not sure if tablebases are productive or counter productive here because with tablebases you do not need to search all the way to mate to see the mate in 10 so there is a reason that it may be easier with tablebases. I think that programs that use tablebases correctly are going to find it faster and I expect chest to find mate in 10 faster after tablebases are implemented in it. Uri
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