Author: Robert Hyatt
Date: 09:01:00 05/11/98
Go up one level in this thread
On May 11, 1998 at 10:15:15, Vincent Diepeveen wrote: > >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 This is baloney. I suppose you are ready to sit down and play someone like Karpov a match, and thoroughly trounce him? Because "his selective search extensions can in no way compensate for the extra plies of full-width you get over him?" That's silly. To characterize Crafty, I generally hit 12-13 plies in the middlegame of a 40/2 game, using my 4 processor machine. I search to an average depth during those 12 ply iterations of maybe 18-20 plies. This counts the many paths that are extended, plus the captures tacked on to the end. DB goes about 10 plies deeper on average. Still 11-12-13 plies depending on the position, but their extensions are *much* more significant fraction of their total search than mine are. Since you haven't played them ever, your comments are forgivable. But once you have played against them, you realize *just how much more they are seeing than you do*... by watching when *they* fail high, then seeing how many full moves before *you* fail high. Remember the bishop trap against Cray Blitz in 1989, where they saw it 10 full *moves* before CB did. And in 1989 CB was *not* slow by any standard of measure. In Cape May, *Socrates was out-searching them by 1-2 plies, yet when it got "interesting" they saw something maybe 10 moves before *socrates* did, because they were searching deeply along the *right* paths. They search deeply along lots of wrong paths to be sure, but they have the horsepower to get away with that where we can't... But they are *most impressive* when you sit across from them and watch *their* output and *your* output. And you realize just how "small" your search tree is compared to theirs...
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