Author: Vincent Diepeveen
Date: 07:15:15 05/11/98
Go up one level in this thread
On May 11, 1998 at 09:46:09, Amir Ban wrote: >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. If you look to the final position that Db prints out, then you see that the king ain't covered by pawns. In the past i gave this terrible penalties. Also something i still do is: giving freepawns that are covered by a pawn huge bonuses. It is clear in this game that DB doesn't do this (the fact that it played Nf5! is my proof, when i remove some bonuses for pawncovered freepawns, then Diep plays Nf5 too). The both of 2 gives you this result. >>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. Well if i allow diep to search a night with nullmove turned on, then it gets more like 18-20 ply here. The better your evaluation, the better your branching factor, is the experience with Diep, although objectively a branching factor should be independant from the evaluation. Guess it has to do with that you have a more accurate score for leaves, where programs not getting this, have q-search problems: another ply changes score from <= alfa to >= beta. So if they say that after this 11 ply they get another 4 ply from the processors, then this still says nothing. I get 18 ply easily after a night, and no extension makes up for that extra positional insight. Also in all these positions you can correctly nullmove, because there are no threats that cannot be seen, assuming you do checks in your q-search. >Amir
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