Author: Uri Blass
Date: 17:09:57 02/27/06
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On February 27, 2006 at 14:53:26, Robert Hyatt wrote: >This will be relatively short and sweet. > >As most know, I've been doing some major revisions to Crafty, preparing for the >next WCCC event. These revisions are affecting the evaluation code which has >been really ripped asunder and partially restored to sanity, and the search >which includes some new reduction code replacing the older futility pruning done >near the frontier, where the reduction stuff is done almost everywhere. > >I knew there would be a few eval issues as king safety has mainly been >simplified with a couple of glaring holes left open for later work. I was >really interested in the new search code because the speed/depth looked very >good. > >So I'll start there, briefly. I've tested the new code in lots of nunn-type >matches, as well as in test suites. So far, the new search solves every >tactical suite I have tried in less total time than previous versions, which was >surprising since the late move reduction idea often delays tactical solutions by >hiding some strange threat moves that get reduced and therefore look >ineffective. But happily, it has gotten better tactically in the same time >frame. Yes it might take an extra ply or two to find the key move, but it is >getting those 1-2 extra plies done more quickly so that the key move is _still_ >found faster than the older versions. So that looks good (so far). > >Another thing I watched for was for a sudden "fail low" to pop up unexpectedly >in a game, and I didn't see a one. Yes we had fail lows, but they were >progressive and were the result of bad positions getting worse, not being +1 and >suddenly seeing -3 after our opponent made an unexpected move. So for the >moment, the current search appears to be solid. I have spent a ton of time on >it in past weeks running test matches against older versions, running test >suites and going over the output carefully, etc. > >Now I'm back to finishing up the eval. > >If you look at the Rascal game (round 8 I think) Crafty played a really lousy >move 28. Nh7+. After looking at this a bit, white has two choices. The knight >must move (attacked by pawn) and it can retreat to f3 (sane) or check on h7 and >get trapped (insane). I agree that 28.Nh7+ was probably not good but the knight does not get trapped(it only cannot move from that square but black has no way to capture it). I see no forced line that win material for black and crafty drew the game. Many programs including commercial programs have positive score for white after Nh7+. Note that I say that Nh7+ is probably not good because I am not sure about it and it is possible that there is something that I do not see and deep search can get the knight out of h7. Uri
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