Author: Omid David Tabibi
Date: 14:21:14 10/21/03
Go up one level in this thread
On October 21, 2003 at 14:43:45, Robert Hyatt wrote: >On October 21, 2003 at 11:53:02, Tord Romstad wrote: > >>I don't run my engine through WAC very often, but before releasing a new >>version (which I will do within a couple of days) I run the whole suite as >>a sanity test. This time, the following position made me worried: >> >>[D]8/8/2Kp4/3P1B2/2P2k2/5p2/8/8 w - - bm Bc8; id "WAC146"; >> >>Previously, my program had no problems with this position. The new >>version, which is the first one to include tablebase support, prefers >>Bd3 instead of Bc8. At ply 21, the score is +12 for white. When I >>disable tablebases, the program plays Bc8. >> >>Does Bd3 also win, or should I look for yet another bug? > >Bd3 is a second solution. It has been in my version of the test since >I first found this myself, years ago. > > >> >>One of the hardest positions in WAC for my engine is number 163: >> >>[D]5rk1/2p4p/2p4r/3P4/4p1b1/1Q2NqPp/PP3P1K/R4R2 b - - bm Qg2+; id "WAC163"; >> >>On a Pentium IV 2.4 GHz, I need 11 plies and 1m53s to find the winning move. >>The problem is to find the line 1... Qg2+ 2. Nxg2 hxg2+ 3. Kxg2 Bf3+ 4. Qxf3 >>exf3+ 5. Kg1 Rf5! followed by Rfh5. Without nullmove pruning, this position >>is solved within a few seconds. >> >>This is rather annoying, as I have lost more games than I would like on >>the ICC because of missing similar tactics. Are there any inexpensive >>tricks to help me solve this kind of positions more quickly? > > >I pick this up at depth=9, time = 2 seconds (using one cpu on my dual 2.8 >xeon box). All I can guess is that I do extensions a bit differently, >somehow, or the adaptive null-move R=3~2 idea helps a bit. I would attribute it to Crafty's extensions. You allow more than one ply of extension at a time (e.g., mate_threat + checking_move) while most programs don't practice it. Additionally, you also do one reply extension, which in this position certainly helps. Based on their analysis, it seems that most commercial engines prefer to keep the branching factor smaller than to extend intensively (Hiarcs is the big exception of course). After some tests I limited the extension to one ply at a time in my engine, and also removed one reply extensions. It seems that the overhead is too much in most cases to justify the profit (especially if you already have some form of checks in quiescence). > > >> >>Tord
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