Author: Vincent Diepeveen
Date: 15:31:58 12/21/99
Go up one level in this thread
On December 21, 1999 at 17:44:06, Robert Hyatt wrote: >On December 21, 1999 at 17:02:53, Greg Lindahl wrote: > >>On December 21, 1999 at 16:18:27, Albert Silver wrote: >> >>>That's correct, he says it was done through software: "During the 1997 match, >>>the software search extended the search to about 40 plies along the forcing >>>lines, even though the nonextended search reached only about 12 plies." He also >>>mentions that "The software portion of the search can be arbitrarily selective >>>without slowing down the system." >> >>If you read the beginning of that paragraph, Hsu explicitly says that the 8 >>plies of software search included forcing. Hsu doesn't say if the final 4 plies >>of hardware search included forcing by droping back to software or not. Given >>that the chess chips seem to operate in an embarrassingly parallel fashion, I >>would suspect that there was no forcing for those plies. Someone could always >>ask Hsu... >> > > > >Old news. The first 4 plies (+ whatever extensions were used) were done on a >single SP processor. The next 4 plies + whatever extensions were triggered were >done in parallel on the SP, which (if stated simply) says that the first 8 >plies, plus all the extensions, are done on the general-purpose SP hardware. >The _final_ 4 plies, plus the capture search were done on the chess processors. >The chess processors _did_ do extensions, but not singular extensions. IE Ken >Thompson did the usual in-check and recapture extensions in Belle, and the >first deep thought (chiptest) chip was nothing more than "belle on a chip". > >Also, chess is _far_ from "embarassingly parallel". It is one of the more >difficult-to-program parallel algorithms, because alpha/beta is a strictly >defined sequential algorithm. Doing it in parallel invites a lot of extra >work that can't be avoided. I couldn't say it better Bob! >>How important is forcing in shallow plies verses deeper plies? That's easy to >>examine using a program. >> >>-- greg > > >Hsu would _like_ to have been able to do singular extensions in hardware. But >there was simply not enough space on the chip as things get _very_ complex >compared to a simple alpha/beta hardware design... > >But you have to ignore some of Vincent's ramblings about DB's search depth. I >once posted a position where they found a forced win of material OTB vs Cray >Blitz, as but one example of their extreme tactical strength. _NOBODY_ found >that win OTB, or overnight. Many liked the move, but _nobody_ saw the tactical >consequences that were forced. They have done this _many_ times over the >years. So I'd say their "11-ply search" is _far_ better than our 14-15 ply >searches, no questions asked... Bob, i explained that the c5 move was because of a horizon effect in deep blue. Diep had the same horizon effect too when i added the extension. Secondly an optimistic evaluation function or a program doing the Rxa4 in the quiescencesearch is gonna find things a lot faster than a smart qsearch that is not doing Rxa4 in the qsearch. Before this gets a blindfolded discussion, first here the position: black timeleft=27:46.40.00 r = - = - b k = Qa7-e3 20 Rf8-a8 = - = - = r o o c2-c3 21 Qb4-b7 - B o o b o - = Rf1-f2 22 Qb7-a7 = - = - n - = - Qe3xa7 23 Ra8xa7 N = - = - = - = Bf4-e3 24 Ra7-a5 = O O - = - = - Be3-b6 25 Ra5-a8 O = B = - R O O Bd3-c2 26 Be7-f8 = - = - R - K - Rd1-e1 27 ... white timeleft=27:46.40.00 black to move Note that it's smarter to get the last few moves for repetitions, that speeds up the search proces *considerable*, as last few moves were not exactly the most exciting moves. r4bk1/5rpp/1Bppbp2/4n3/N7/1PP5/P1B2RPP/4R1K1 b - - the main idea in this position is that after c5 the bishop on b6 is more or less hung. Now this doesn't mean that black sees the forced win, because seeing a forced win here means +5.0. What is the problem here? Well the big problem for nowadays smart programs is that after a couple of moves there goes a rook to b7 and white for some reasons must move a rook to b-file. all bishops are gone then from their places which allows Rxa4 bxa4 Rxb1 in quiescencesearch. However not all programs play Rxa4 in qsearch. Just get away the c2 bishop and the b6 bishop and put the white rook to b2 and the black rook to b7. Not many programs will play Rxa4 here in quiescencesearch, as that's covered by a pawn, meaning an exchange gets lost. The score of Deep Blue here is however based upon a horizon effect which i posted a couple of time ago. This doesn't take away that *all* programs will play c5 here with a good score for black. Nowadays DIEP is very optimistic in such endgames too. Let's see whether i can get the same high score with the normal version of DIEP here searching fullwidth...
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