Author: Tord Romstad
Date: 13:31:11 10/21/03
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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. I'm relieved to hear that. I will add this solution to my EPD file. >>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 tried changing from R=3 to R=2, and that just resulted in an even slower solution. However, I found that searching checks in qsearch in the endgame (normally I only do this in the middle game) helps. With checks in qsearch enabled in the endgame, I need 8 plies and 2 seconds. I'm afraid this will slow me down too much in other endgame positions, though. I'll probably have to play around a bit with my extensions and see if I can find some other way to find Qg2+ reasonably quickly. Thanks for your answer, and thanks to Uri for all the data for other engines! Tord
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