Author: Amir Ban
Date: 06:46:09 05/11/98
Go up one level in this thread
On May 11, 1998 at 08:41:11, Vincent Diepeveen wrote: > >On May 11, 1998 at 07:04:23, Amir Ban wrote: > >>On May 10, 1998 at 18:51:35, Vincent Diepeveen wrote: >> >> >>This position was analyzed much more deeply than this. >> >>After 36.Qb6, Rd8 is indeed best, but DB did not consider it but >>36...Qe7 (I posted the complete analysis recently). After 36... Rd8 >>37.axb5, a micro will quickly see that white is in trouble, but after >>36...Qe7 37.axb5, black is a full pawn worse because of the need to >>protect the bishop on d6. Justifying 36.axb5 if you do not consider Rd8 >>is more than a few tenth of a pawn to justify, actually it's about a >>full pawn. >> >>Why didn't DB consider Rd8 ? Probably it saw 36. Qb6 Rd8 37.Be4 ! and it >>seems black is screwed. But black has a fantastic resource: 37... a5! >>38.axb5 axb4!! sacing a piece, to get the queen to the first rank and >>force a draw on perpetual threats (echo of the final position, but more >>complicated). > >It is clear that DB didn't see the piece sac, because this line is way >longer >than the 23 ply (Diep needs) to see that Kf1? leads to a draw and Kh1! >wins the game. > Right. A human may play it on a hunch that things will work out, specially if he's desperate. >In the line you posted i see that DB score doesn't get to zero, but >just goes down few tens of a pawn. So that'll be some king safety, >no doubt. > King safety no doubt, but how much ? This was already discussed here last year. Even CSTal had problems justifying the evaluation. > >I was surprised seeing in the lines you posted here that DB just got 11 >ply. > >Although i admit that when i would search fullwidth with SE and all kind >of check/threat extensions i doubt whether i would get more with >around 70 Billion nodes. > Yes. Actually the log says iteration not ply, but my guess is that this is the brute-force ply depth. We are spoiled by null-move depths, but DB don't do that, and they don't believe in pruning either. I think a micro with full width search + regular extensions would just barely reach 8 ply in this position. 11 ply is slightly lower than I expect, but remember this is a tough position for DB with the eval going up and down like crazy. Some people suggest you should add 4 ply for the leaf processors, but arithmetic tells me that 15-ply brute force is stretching credulity. Amir
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