Author: Vincent Diepeveen
Date: 07:15:40 06/27/98
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Hello Bob you're lately telling us a lot of new facts, I remember that some time ago (2 years perhaps?) we already knew the DB speed. i claimed that getting 18-20 ply would be no problem for them if they stripped some extensions, improved move ordering and used nullmove. At that time you told your audience that getting 20 ply was *impossible* and challenged me. Right now my program GETS 20 ply in several middlegame positions after 24 hours of analyses (and i'm not referring to positions where you need to make a forced move like recapture), but i'm also in the pruning buiseness, so probably this doesn't count in your eyes as some stupid variations get pruned by Diep. Note that very important is the fact that i'm having 80MB of ram now, under NT i use 60MB of hash under DOS 64MB. It appeared that big hashtables at analysis level give a lot (which is rather unsurprising). Now how big was my surprise when reading next: >Again... if DB used null-move R=2, with a search like mine, they would do 20+ >plies in middlegame. They do extensions instead. I do 12 plies at 200K nodes How can they at hardware which is slower than was expected few years ago (i still remember an email from one of the teammembers very well where they expected to make a chip which got 5-10M nodes a second, and that has become finally 2.5M) get suddenly 20+ ply without my 'dubious' forward pruning, but with the stuff discusses in RGCC, and they even could search deeper in your opinion? This needs some explanation! >per second. They are 1,000 times faster... with a branching factor of roughly >2.5, what is log base 2.5 of 1000? That's my search depth at that speed. So >*obviously* they are doing something else. You compare your 12 plies to their >12 plies. I say that's total hogwash. Ok ask IBM for old printouts of the match and we can easily compare their mainlines to our mainlines. Don't do whether their 12 ply is in fact 24 ply or 13 ply. 12 ply is 12 ply, if you use nullmove you run zugzwang risks. If you don't do checks in q-search you even miss obvious mate threats last couple of ply, if you prune a lot you might sometimes miss something like heavy sacraficing for a mating attack; but lucky none of this all happened in the games. Their 12 ply aren't more holy than mine 12 ply. I admit: i prune, so certain stupid lines which might win might get pruned. There were no difficult ! moves played by Deep Blue, no difficult sacrafices, no mate in 40 announced, and win in 23 ply (23 ply for Diep: Kf1? in game II, where Kh1! wins forced) was missed by Deep Blue. Yet it plays a horrible move which is only 1 ply deep (12.Bxg6? in game 4 after the moves: 1. e4 c6 2. d4 d6 3. Nf3 Nf6 4. Nc3 Bg4 5. h3 Bh5 6. Bd3 e6 7. Qe2 d5 8. Bg5 Be7 9. e5 Nfd7 10. Bxe7 Qxe7 11. g4 Bg6 12. Bxg6 hxg6) This move Bxg6 can be easily prevented if a program knows that after hxg6 the simple pattern g6,g7,f7 open h-file is not a bad doubled pawn. This is a beginners fault of 1 ply. So how deep did Deep Blue search? Please test your programs at it. If i remember well this pattern is also in psion. Vincent
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